Substitution of Cr in place of Al in the framework of molecular sieve via treatment with fluoride salts

ABSTRACT

Molecular sieve compositions are prepared by extracting aluminum and substituting chromium and/or tin for extracted aluminum to give molecular sieve products containing framework chromium and/or tin atoms. The process of preparing the chromium and/or tin-containing molecular sieves invovles contacting a starting molecular sieve with a solution or slurry of at least one of a fluoro salt of chromium or a fluoro salt of tin under effective process conditions to provide for aluminum extraction and substitution of chromium and/or tin. These compositions are effective as hydrocarbon conversion catalysts and for separating mixtures of molecular species.

CROSS REFERENCE TO RELATED APPLICATION

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 07/450,931 filed on Dec. 4, 1989 which in turn is acontinuation-in-part of U.S. patent application Ser. No. 07/133,372filed on Dec. 15, 1987, now abandoned.

FIELD OF THE INVENTION

The instant invention relates to molecular sieve compositions, themethod for their preparation and to processes employing them. Moreparticularly it relates to molecular sieve compositions topologicallyrelated to prior known molecular sieves but which are characterized ascontaining framework atoms of of chromium, and preferably having a verylow content of defect sites in the structure, as hereinafter disclosed.In general the preparative process involves contacting a molecular sievepreferably with an aqueous solution of of a fluoro salt of chromium,preferably a fluoro salt which does not form insoluble salts withaluminum, under conditions suitable to insert chromium for aluminum inthe framework.

BACKGROUND OF THE INVENTION

The crystal structures of naturally occurring and as-synthesizedzeolitic aluminosilicates are composed of AlO₄ ⁻ and SiO₄ tetrahedrawhich are cross-linked by the sharing of oxygen atoms. The term AlO₄ ⁻,SiO₄ and the like, are used to depict the tetrahedral atoms Al, Si andothers, in four-fold coordination with oxygen, within the framework ofthe zeolite. It is understood that each of the four oxygen atoms thusdepicted is linked to an additional tetrahedral atom, thus completingthe charge requirements placed on each tetrahedral unit. Theelectrovalence of each tetrahedron containing an aluminum atom isbalanced by association with a cation. Most commonly this cation is ametal cation such as Na⁺ or K⁺ but organic species such as quaternaryammonium ions are also employed in zeolite synthesis and in someinstances appear as cations in the synthesized product zeolite. Ingeneral the metal cations are, to a considerable extent at least,replaceable with other cations including H⁺ and NH₄ ⁺. In many instancesthe organic cation species are too large to pass through the pore systemof the zeolite and hence cannot be directly replaced by ion exchangetechniques. Thermal treatments can reduce these organic cations to H⁺ orNH₄ ⁺ cations which can be directly ion-exchanged. Thermal treatment ofthe H⁺ or NH₄ ⁺ cationic forms of the zeolites can result in thesubstantial removal of these cations from their normal association withthe AlO₄.sup. - tetrahedra thereby creating an electrovalent imbalancein the zeolite structure which must be accompanied by structuralrearrangements to restore the electrovalent balance. Commonly when AlO₄⁻ tetrahedra constitute about 40% or more of the total frameworktetrahedra, the necessary structural rearrangements cannot beaccommodated and the crystal structure collapses. In more siliceouszeolites, the structural integrity is substantially maintained but theresulting "decationized" form has certain significantly differentproperties from its fully cationized precursor.

The relative instability of aluminum in zeolites, particularly in thenon-metallic cationic or the decationized form, is well recognized inthe art. For example, in U.S. Pat. No. 3,640,681, issued to P. E.Pickert on Feb. 3, 1972, there is disclosed a process for extractingframework aluminum from zeolites which involves dehydroxylating apartially cation deficient form of the zeolite and then contacting itwith acetylacetone or a metal derivative thereof to chelate andsolubilize aluminum atoms. Ethylenediaminetetraacetic acid has beenproposed as an extractant for extracting aluminum from a zeoliteframework in a process which is in some respects similar to the Pickertprocess. It is also known that calcining the H⁺ or NH₄ ⁺ cation forms ofzeolites such as zeolite Y in an environment of water vapor, eitherextraneous or derived from dehydroxylation of the zeolite itself, iseffective in removing framework aluminum by hydrolysis. Evidence of thisphenomenon is set forth in U.S. Pat. No. 3,506,400 issued Apr. 14, 1970to P. E. Eberly, Jr. et al.; U.S. Pat. No. 3,493,519, issued Feb. 3,1970 to G. T. Kerr et al.; and U.S. Pat. No. 3,513,108, issued May 19,1970 to G. T. Kerr. In those instances in which the crystal structure ofthe product composition is retained after the rigorous hydrothermaltreatment infrared analysis indicated in the presence of substantialhydroxyl groups exhibiting a stretching frequency in the area of about3740, 3640 and 3550 cm⁻¹. The infrared analytical data of U.S. Pat. No.3,506,400 is especially instructive in this regard. An explanation ofthe mechanism of the creation of these hydroxyl groups is provided byKerr et al. in U.S. Pat. No. 3,493,519, wherein the patentees state thatthe aluminum atoms in the lattice framework of hydrogen zeolites canreact with water resulting in the removal of aluminum from the latticein accordance with the following equation: ##STR1##

The aluminum removed from its original lattice position is capable offurther reaction with cationic hydrogen, according to Kerr et al. toyield aluminum-containing i.e., hydroxoaluminum, cations by theequation: ##STR2##

It has been suggested by Breck, D. W. and Skeels, G. W., "ZeoliteChemistry II. The Role of Aluminum in the Hydrothermal Treatment ofAmmonium-Exchanged Zeolite Y, Stabilization", Molecular Sieves - II, A.C. S. Symposium Series 40, pages 271 to 280 (1977), that stabilizationof NH₄ Y occurs through hydrolysis of sufficient framework aluminum toform stable clusters of these hydroxyaluminum cations within thesodalite cages, thereby holding the zeolite structure together while theframework anneals itself through the migration of some of the frameworksilicon atoms.

It is alleged in U.S. Pat. No. 3,594,331, issued Jul. 20, 1971 to C. H.Elliott, that fluoride ions in aqueous media, particularly underconditions in which the pH is less than about 7, are quite effective inextracting framework aluminum from zeolite lattices, and in fact whenthe fluoride concentration exceeds about 15 grams active fluoride per10,000 grams of zeolite, destruction of the crystal lattice by thedirect attack on the framework silicon as well as on the frameworkaluminum can result. A fluoride treatment of this type using from 2 to22 grams of available fluoride per 10,000 grams of zeolite (anhydrous)in which the fluorine is provided by ammonium fluorosilicate is alsodescribed therein. The treatment is carried out for the purpose ofimproving the thermal stability of the zeolite. It is theorized by thepatentee that the fluoride in some manner becomes attached to theconstructional alkali metal oxide, thereby reducing the fluxing actionof the basic structural Na₂ O which would otherwise result in thecollapse of the crystal structure. Such treatment within the constraintsof the patent disclosure has no effect on either the overall siliconcontent of the zeolite product or the silicon content of a unit cell ofthe zeolite.

Since stability is quite obviously, in part at least, a function of theAl₂ O₃ content of the zeolite framework, it would appear to beadvantageous to obtain zeolites having lower proportions of Al₂ O₃ whileavoiding the structural changes inherent in framework aluminumextraction. Despite considerable effort in this regard, however, onlyvery modest success has been achieved, and this has applied to a fewindividual species only.

A process for increasing the SiO₂ /Al₂ O₃ ratio in zeolites is disclosedin: commonly assigned U.S. Pat. No. 4,503,023, issue date Mar. 5, 1985;commonly assigned U.S. Pat. No. 4,610,856, issue date Sep. 9, 1986, U.S.Pat. No. 4,711,770, issue date Dec. 8, 1987 (U.S. patent applicationSer. No. 880,103 filed Jun. 30, 1986), and in Skeels, G. W. and Breck,D. W. "Proceedings of the Sixth International Zeolite Conference",edited by David Olson and Attilio Bisio, Butterworth & Co. Ltd. pages 87to 96 (1984). The process disclosed therein comprises inserting siliconatoms as SiO₄ tetrahedra into the crystal lattice of an aluminosilicatehaving a SiO₂ /Al₂ O₃ molar ratio of at least 3 and pore diameters of atleast 3 Angstroms with a fluoro-silicate salt in an amount of at least0.0075 moles per 100 grams of the zeolitic aluminosilicate on ananhydrous basis, said fluorosilicate salt being in the form of anaqueous solution having a pH value within the range of 3 to about 7 andbrought into contact with the zeolitic aluminosilicate at a ratesufficiently slow to preserve at least 60 percent of the crystallinityof the staring zeolitic aluminosilicate.

Commonly assigned European Patent Application Serial No. 85,902,354.1describes ammonium fluoride salts of the metal cations iron and/ortitanium which are used to treat the zeolites in an aqueous medium.Framework aluminum is complexed by the fluoride and removed from thezeolite. The metal cation is inserted into the framework in place of thealuminum.

Various attempts have been made to substitute chromium or tin into azeolite framework via primary synthesis methods but none have been trulysuccessful so far. Attempts to synthesize zeolites of the pentasilfamily of zeolites (ZSM-5 like) with a number of ions other thanaluminum have been made. In some cases chromium or tin is found with thezeolite but not in the framework of the zeolite. The likelihood thateither chromium or tin is not a part of the zeolite framework in primarysynthesis products rests on the fact that such a high pH is required forsynthesis that it is probable that the chromium or tin are present asoxides and/or hydrous oxides. For example, in U.S. Pat. No. 4,405,502(Klotz) discloses the presence of up to 12.40 weight percent of Cr₂ O₃with the crystalline chromosilicate (Example IV), but the Cr₂ O₃ in theproduct is present as amorphous or crystalline oxides. The examplesteach that the chromium, initially dissolved in water, is rapidlyprecipitated as the hydroxide before ever coming in contact with thesilica source. Further, "these results show that as the chromium factorbecame larger, more and more Cr₂ O₃ was detected in the product."(Column 24, lines 15-17.)

Marosi et al., in German Patent No. 2,831,630, disclose the presence ofbetween 0.50 weight percent and 3.00 weight percent of Cr₂ O₃ with aZSM-5 type structure. The amount of chromium that would be included inthe framework of the ZSM-5, if indeed it were located therein, wouldrange from 0.4 to 2.5 atoms out of 100 framework tetrahedral atoms. Inthe only Example where a product composition is given (1), the solidproduct would contain only 0.7 Cr atoms out of 100 in the framework, avalue less than the compositions of the present invention. In Example 2in U.K. Patent Application GB 2,024,790, (Taramasso et al.), a 6.00weight percent of Cr₂ O₃ with a ZSM-5 type structure was obtained andwhich was designated "TRS-28". While the claims teach that the chromiumatoms either, "entered the crystalline lattice in place of siliconatoms" or "in the form of salts of bisilicic or polysilicic acids", theevidence presented in the examples fairly teach that the chromium is notwithin the lattice framework of the ZSM-5 product. Surface areas of allof the products of the invention are given which indicate that there isa substantial reduction relative to a typical ZSM-5. This is evidence ofsome amorphous or dense phase present with the zeolite. Typically ZSM-5or its more siliceous analog silicalite will have a surface area, (BET),of greater than 400 square meters per gram. The chromium containingproduct of the U.K. patent application GB 2,024,790, had a surface area(BE) of 380 square meters per gram, a value at least 5% less than whatmight be expected of a pure zeolite sample. Additionally, the chromiumcontaining product of said invention containing 6.0 weight percent Cr₂O₃ would be expected to have an ion exchange capacity of 0.79 meq/gram,providing all of the chromium atoms were to be positioned in theframework in tetrahedral coordination with four oxygen atoms. However,only 0.0058 meq/gram of cations were actually found in the calcined(550° C.) product, a value at least two orders of magnitude less thanwhat would be necessary to balance the framework negative charges, ifchromium were indeed in the framework. In order for chromium to be inthe framework in tetrahedral coordination with four oxygen atoms, it isa requirement that there be present a positively charged species orcation in order to balance the negative charge caused by the presence ofthe trivalent chromium ion sharing the negative charges on four separateoxygen atoms with silicon. Lacking the cation, it is not possible forthe chromium to be tetrahedrally coordinated with oxygen in this way andhence, the chromium of this example is not in the framework of thezeolite synthesized in the example. The converse is not necessarilytrue, namely, that if a positively charged cation is found to balancethe negative charge on the chromium to satisfy the requirement oftetrahedral coordination with oxygen, that the chromium is in theframework. It would be evident that the chromium is in tetrahedralcoordination with oxygen, but it does not necessarily prove that thechromium is located in the zeolite framework. It is probable that, likeamorphous aluminosilicates, the amorphous chromosilicates can havetetrahedrally coordinated chromium atoms and hence ion exchangecapacity.

European Patent Application 13,630 (Rubin et al.) discloses the presenceof between 0.63 weight percent and 2.90 weight percent of Cr₂ O₃ with aZSM-12 type structure. The samples described in the Tables of the patentapplication, particularly the products containing chromium, show asubstantial loss of surface area. This indicates that the purity of theas-synthesized products is questionable and that they must containamorphous material. A relative relationship can also be found in theTables, namely that as the chromium content of the synthesis productincreases, the reported X-ray crstallinity decreases.

In European Patent Application 14,059 (Rubin et al.) between 0.09 weightpercent and 1.26 weight percent of Cr₂ O₃ with a ZSM-11 type structurewas obtained. Similar observations can be made with these products; thatthe products containing chromium have reduced X-ray crystallinity,substantially reduced adsorption capacity for n-hexane and cyclohexaneand substantially lower surface areas when compared to a product whichdoes not contain chromium. Each observation taken alone would notpreclude the incorporation of chromium in the ZSM-11 framework. However,taken together, these data are substantive evidence for theprecipitation of an amorphous chromium containing phase with thezeolite, which under the very basic synthesis conditions employed is theexpected result.

Dwyer et al. in U.S. Pat. No. 3,941,871 disclose the presence of tin inplace of or as part of the organic template in a ZSM-5 type of asturcture but not as a part of the ZSM-5 framework structure itself. InU.S. Pat. No. 4,329,328 (McAnespic et al.) the synthesis of astannosilicate is suggested, but no examples of such synthesis are givenor are any properties of such materials suggested.

The above-mentioned references, while they may suggest the incorporationof the chromium or tin metal ions into the frameworks of the respectivezeolites, provide consistent evidence that the metal ions are notincluded in the framework, and are merely precipitated with the zeoliteas some other probably amorphous phase during the course of thesynthesis process. Tiele et al. in "Proceedings of the InternationalSymposium on Zeolite Catalysis", Siofok, Hungary, May 13, 1985,commented on isomorphic substitution in zeolites, stating that,"Generally speaking these new materials are claimed based upon theirnovel chemical composition or XRD spectrum or both. This novelty doesnot necessarily mean that the new materials contain the new element, orat least part of it, substituted in the zeolite framework. As far as weare aware, only in the case of boron substitution sound proof isavailable for its presence in the zeolite lattice." The reason for thisfailure is then obvious, since the very synthesis conditions used tosynthesize the zeolite products are such that a nearly insoluble metalhydroxide precipitates thereby limiting the ability of the metal oxideto incorporate into the silicate units during crystal growth. Thisfeature was only recently pointed out by Szostak et al. in Journal ofChemical Society, Faraday Trans. I, page 83 (1987). By recognizing thecritical nature of the pH they were able to, for the first time,synthesize the ferrisilicate analog of ZSM-5.

It should be further pointed out that Tielen at the top of page 9 states"based on this table and the evidence mentioned in the introduction,elements with ionic radii between 0.020 and 0.061 are potentialcandidates for incorporation into a framework . . . ". Using the valuesgiven for the Shannon references (radii in tetrahedral coordination) itis observed that Sn⁺⁴ has an ionic radius of 0.069 nm or 0.69 Å (notethat Shannon reports this value as the crystal radii) which is outsidethe range stipulated by Tielen and thus would not be expected to be inthe framework. Although values for Cr⁺³ and Sn⁺² are not provided inTielen, they are provided by R. D. Shannon in his original paper (ActaCryst. A 32, 751-767 (1976) as Cr⁺³ =0.755 and Sn⁺² =1.36. It should benoted that the values for Cr⁺³ and Sn⁺² are for octahedral coordinationand the number for tetrahedral coordination would be expected to besmaller. Further, the numbers presented by Tielen are the crystal radii(see Shannon Table 1, page 752). Accordingly, none of these metal ionswould be expected to be in the framework.

Another reference which has been cited in this art is Canadian Pat. No.1,127,134 to Morrison. This reference discloses an "Alumino-silicatezeolite" which contains a metal oxide selected from the group consistingof indium, boron, ruthenium, platinum, chromium, rare earth, vanadium,palladium, molybdenum, mercury, tellurium, silver and mixtures thereof.However, there is no mention or hint that these metals are or could bein the framework. Indeed, on page 6, lines 1-7, the patentees state thatit is not known whether the metal is present as a metal or as a metalcompound. Given this uncertainty, it would be pure speculation to statethat Morrison discloses an aluminosilicate zeolite where some of thealuminum in the framework has been replaced by chromium or some othermetal. Accordingly, there is nothing in Morrison that suggests a zeolitehaving chromium as a framework metal.

The above mentioned references do suggest that it is desirable tosynthesize zeolites or molecular sieves containing chromium or tin inthe framework tetrahedral sites. However the methods employed in thereferences leave little doubt that the metal has been deposited with thezeolite either as an oxide or hydroxide or as an amorphous metalsilicate. The references further demonstrate the difficulty involved inthe incorporation of these metal ions in the zeolite tetrahedralframework positions. The uniqueness of the method of the currentapplication which relies on the solubility of the chromium and tin metalions in an acidic medium, and the Secondary Synthesis procedure toincorporate the metal ions into the framework is further demonstrated.As for the obviousness of the Secondary Synthesis procedure toincorporate any metal ion into the framework of an existing zeolite, allattempts to use this process with the ions of phosphorus or boron havethus far been unsuccessful. Boron is the only metal ion thus far thathas been successfully incorporated into the pentasil zeolite frameworkvia primary synthesis methods (Tielen et al.). Only by careful controlof the Secondary Synthesis conditions can one be successful inincorporating iron and/or titanium (D-13733), or chromium and/or tininto the framework of existing zeolites or molecular sieves.

Secondary Synthesis as used herein means a process whereby a molecularsieve product is treated by some method (Secondary Synthesis) to obtaina molecular sieve product that is either not obtainable by primarysynthesis methods or is prepared with great difficulty or is notnormally found in nature.

The present invention relates to novel zeolite compositions whichcontain significant framework tetrahedral atoms, which are not found toany significant level either in naturally occurring zeolites or insynthetic zeolites.

In the present invention, zeolite Y, zeolite L, mordenite and zeoliteLZ-202 (an omega type zeolite prepared without the use of a templatingagent as disclosed in U.S. Pat. No. 4,840,779) are treated with aqueousammonium fluoride salts of either or both chromium or tin. During thetreatment aluminum is removed from the molecular sieve framework and themetal ions is incorporated therein. By means of this invention, themetal ions of chromium and/or tin can be incorporated into molecularsieve frameworks where they are not normally found in nature.

DESCRIPTION OF THE FIGURE

FIG. 1 is a ternary diagram wherein parameters relating to the instantcompositions are set forth as mole fractions.

SUMMARY OF THE INVENTION

A molecular sieve composition having a three-dimensional microporousframework structure which has an unit empirical formula on an anhydrousbasis of:

    (M.sub.w Al.sub.x Si.sub.y)O.sub.2

where "M" is at least one of chromium or tin; and "w", "x" and "y"represent the mole fractions of "M" , aluminum and silicon,respectively, present as framework tetrahedral oxide units said molefractions being such that they are within the triagonal area defined bypoints, A,B, and C of FIG. 1.

A process for preparing molecular sieve composition containing at leastone of chromium or tin from a starting crystalline microporousaluminosilicate having a framework structure comprising aluminum andsilicon present as tetrahedral oxides which comprises contacting saidcrystalline aluminosilicate having pore diameters of at least about 3Angstroms and having a molar SiO₂ Al₂ O₃ ratio of at least 2, with atleast one of a fluoro salt of chromium and a fluoro salt of tin, saidfluoro salt being in the form of a solution or slurry, whereby frameworkaluminum atoms of the zeolite are removed and replaced by at least oneof chromium or tin.

Molecular sieves and the process for their preparation are claimedwherein said molecular sieves have three-dimensional microporouscrystalline framework structures consisting of CrO₄ ⁻, SnO₄ ⁼ or SnO₄AlO₄ ⁻ and SiO₄ tetrahedra which are cross linked by the sharing ofoxygen atoms. These new molecular sieves expressed as mole fractions ofoxides have a unit empirical formula on an anhydrous basis of :

    (M.sub.w Al.sub.x Si.sub.y)O.sub.2

where "M" is chromium and/or tin; and "w", "x" and "y" represent one ofthe mole fractions of "M", aluminum and silicon, respectively, presentas framework tetrahedral oxide units, said mole fractions being suchthat they are within the compositional area defined by points A, B and Cin FIG. 1, where points A, B and C have the following values for "w","x" and "y".

    ______________________________________                                        Mole Fraction                                                                 Point   w              x      y                                               ______________________________________                                        A       0.49           0.01   0.50                                            B       0.01           0.49   0.50                                            C       0.01           0.01   0.98                                            ______________________________________                                    

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to new molecular sieve compositions and tothe processes for their preparation. The molecular sieves of the instantinvention have three-dimensioned microporous crystal framework oxidestructures of "MO₂ ", AlO₂ and SiO₂ in tetrahedral units which have aunit empirical formula on an anhydrous basis of:

    (M.sub.w Al.sub.x Si.sub.y)O.sub.2                         (1)

wherein "M" represents at least one of chromium or tin; and "w", "x" and"y" are as defined above represent the mole fractions of "M", aluminumand silicon, respectively, present as tetrahedral oxides.

The term "unit empirical formula" is used herein according to its commonmeaning to designate the simplest formula where gives the relativenumber of moles of chromium and/or tin (M), aluminum and silicon whichform "MO₂ ", AlO₂, and SiO₂ tetrahedral units within the molecularsieve. The unit empirical formula is given in terms of chromium and/ortin, aluminum and silicon as shown in Formula (1), above, and does notinclude other compounds, cations or anions which may be present as aresult of the preparation or the existence of other impurities ormaterials in the bulk composition not containing the aforementionedtetrahedral units.

The instant process generally comprises a method for removing frameworkaluminum from zeolites having SiO₂ /Al₂ O₃ mole ratios of about 2 orgreater and substituting therefore one or more elements selected fromthe group consisting of chromium and/or tin. The resulting molecularsieves contain chromium and/or tin and have crystal structures similarto that of the initial zeolite.

The process of the invention comprises contacting a crystalline zeolitehaving pore diameters of at least about 3 Angstroms and having a molarSiO₂ /Al₂ O₃ ratio of at least 2, with an effective amount of at leastone of a fluoro salt of chromium or a fluoro salt of tin, preferably inan amount of at least 0.001 moles per 100 grams of zeolite startingmaterial, said fluoro salt being in the form of an aqueous solution orslurry and brought into contact with the zeolite either incrementally orcontinuously at a slow rate (optionally in the presence of a buffer)whereby framework aluminum atoms of the zeolite are removed and replacedby chromium and/or tin atoms. It is desirable that the process becarried out such that at least 60 percent, preferably at least 80percent, and more preferably at least 90 percent of the crystalstructure of the starting zeolite is retained and that the DefectStructure Factor (hereinafter defined) is increased by less than 0.10,and preferably by less than 0.08.

Crystalline zeolite starting suitable for the practice of the presentinvention can be any naturally occurring or synthetically producedzeolite species which have pores large enough to permit the passage ofwater, chromium and/or tin fluoro salts and reaction products throughtheir internal cavity system. These materials can generally berepresented, in terms of molar ratios of oxides, as

    M.sub.2/n O: Al.sub.2 O.sub.3 :xSiO.sub.2 :yH.sub.2 O

wherein "M" is a cation having the valence "n", "x" is a value of atleast about 2, and preferably about 3and "y" has a value of from zero toabout 9. This value of "y" depends upon the degree of hydration and thecapacity of the particular zeolite to hold adsorbed water.Alternatively, the framework composition of the naturally occurring orsynthetic zeolite starting material can be expressed in terms of themole fraction of framework tetrahedra, TO₂, as:

    (Al.sub.a Si.sub.b)O.sub.2                                 (2)

wherein "a" is the mole fraction of framework tetrahedral sites occupiedby aluminum atoms and "b" is the mole fraction of framework tetrahedralsites occupied by silicon atoms. Should the framework of the startingmaterial contain atoms in addition to silicon and aluminum, thesematerials may be similarly expressed in terms of their "TO₂ " formula interms of their fractional occupation of the framework of the startingmaterial. The algebraic sum of all of the subscripts within the bracketsis equal to 1. In the above example, a=b=1.

Representative of the crystalline aluminosilicate zeolite molecularsieves include, but are not limited to erionite, mordenite,clinoptilolite, zeolite Y, zeolite L, zeolite LZ-202 (an omega typezeolite prepared without the use of a templating agent as disclosed U.S.Pat. No. 4,840,779), zeolite omega, zeolite beta, zeolite TMA offretite,LZ-105, ZSM5ZSM-34 and ZSM-35. Zeolite Y is disclosed in U.S. Pat. No.3,130,007; zeolite L is disclosed in U.S, Pat. No. 3,216,789; LZ-105 isdisclosed in U.S. Pat. No. 4,257,885; zeolite omega is disclosed in U.S.Pat. No. 4,242,036; zeolite beta is disclosed in U.S. Pat. No.3,308,069; ZSM-5is disclosed in U.S. Pat. No. 3,702,886; ZSM-34 isdisclosed in U.S. Pat. No. 4,086,186; and ZSM-35 is disclosed in U.S.Pat. No. 3,992,466. Both naturally occurring and synthetically preparedzeolite molecular sieves can be used.

For reasons more fully explained hereinafter, the starting zeoliteshould be able to withstand the initial loss of framework aluminum atomsto at least a modest degree without collapse of the crystal structureunless the process is to be carried out at a very slow rate, or theprocess is to be buffered. In general the ability to withstand aluminumextraction and maintain a high level of crystallinity is directlyproportional to the initial SiO₂ /Al₂ O₃ molar ratio of the zeolite.Accordingly, it is preferred that the SiO₂ /Al₂ O₃ ratio is preferablyat least about 2.0, and more preferably about 3. It is also preferredthat at least about 50 percent, and more preferably at least 95 percentof the AlO₄ ⁻ tetrahedra of the naturally occurring or as-synthesizedzeolite are present in the starting zeolite. Most advantageously thestarting zeolite contains as many as possible of its original AlO₄ ³¹tetrahedra, i.e. the starting zeolite has not been subjected to anypost-formation treatment which either extensively removed aluminum atomsfrom their original framework sites or converts them from the normalconditions of 4-fold coordination with oxygen.

The cation population of the starting zeolite is not a critical factorinsofar as substitution of chromium and/or tin for framework aluminum isconcerned, but since the substitution mechanism may involve the in situformation of salts of at least some of the zeolitic cations, it isgenerally advantageous that these salts be water-soluble to asubstantial degree to facilitate their removal from the molecular sieveproduct. It is found that ammonium or hydronium cations form the mostsoluble salts in this regard and it is accordingly preferred thatpartially or at least 50 percent, most preferably 85 or more percent, ofthe zeolite cations be ammonium or hydronium cations. Sodium, one of themost common cations present in zeolites, is found to form Na₃ AlF₆,which is only very sparingly soluble in either hot or cold water. Whenthis compound is formed as precipitates within the structural cavitiesof the zeolite it is quite difficult to remove by water washing. Itsremoval, moreover, is important if thermal stability of the molecularsieve product is desired since substantial amounts of fluoride can causecrystal collapse at temperatures as low as 500° C.

For purposes of simplifying the description of the products of the aboveprocess, as above defined the framework composition of the zeolitestarting material and the products of the instant process are expressedin terms of mole fractions of framework tetrahedra, i.e., the "TO₂ ",where T represents the substituting tetrahedral atom in the framework.The starting zeolite may be expressed as:

    (Al.sub.a Si.sub.[ ]z)O.sub.2

whereas "a" is the mole fraction of aluminum tetrahedra in theframework; "b" is the mole fraction of silicon tetrahedra in theframework; "[ ]" denotes defect sites in the framework; and "z" is themole fraction of defect sites in the zeolite framework. In many casesthe "z" value for the starting zeolite is zero and the defect sites aresimply eliminated from the expression. Numerically the sum of the valuesa+b+z=1.

If defect sites are present, the molecular sieves of this invention canhave a unit empirical formula expressed in terms of the mole fractionsof framework tetrahedra (TO₂) of :

    [Al.sub.u Si.sub.v M.sub.w[ ]z ]O.sub.2

where u is the mole fraction of aluminum and ranges from about 0.01 toabout 0.5, v is the mole fraction of silicon and ranges from about 0.5to about 0.98, M is chromium, tin or mixtures thereof, w is the molefraction of M and ranges from about 0.01 to about 0.49, [ ] is frameworkdefect sites and z is the mole fraction of defect sites in the frameworkand ranges from greater than zero to about 0.2.

When the molecular sieves of this invention are prepared by the specificprocess of this invention, then the molecular sieve can have a unitempirical formula expressed in terms of the mole fractions of tetrahedra(TO₂) of:

    [Al.sub.(a--N) Si.sub.b M.sub.c[ ]z ]O.sub.2

wherein: "N" is defined as the mole fraction of aluminum tetrahedraremoved from the framework during the treatment; "a" is the molefraction of aluminum tetrahedra present in the framework of the startingzeolite; "b" is the mole fraction of silicon tetrahedra present in theframework of the zeolite; "[ ]" is the framework defect sites; "z" isthe mole fraction of defect sites in the framework and varies fromgreater than zero to about 0.2; "M" denotes chromium and/or tin; and "c"is the mole fraction of chromium and/or tin tetrahedra resulting fromthe fluoro salt treatment of the instant process and varies from about0.01 to 0.5. Numerically, the sum of the values:

    (a-N)+b+c+z=1;

The term "Defect Structure Factor" for any given zeolite is equivalentto the "z" value of that particular zeolite. The net change in DefectStructure Factors between the starting zeolite and the product zeoliteis equivalent "Z".

    z=z(product zeolite)-z(starting zeolite)

Theoretically, there should be no change in the silicon content andtherefore "c" should equal (N-z) where "z" is the net change in the molefraction of defect sites in the zeolite framework resulting from thetreatment. However, in reality fluoride does sometimes react withsilicon of the molecular sieve particularly on the surface of thecrystals of the more siliceous molecular sieves causing etching andtransport of silicon atoms to other defect sites of the crystal. Hence"c" will not always be actually equal to (N-z).

The chromium and/or tin-containing molecular sieve compositions preparedby the instant processes have framework aluminum removed from thestarting zeolite with substitution of chromium and/or tin. The processgenerally comprises:

(a) contacting at effective processes conditions a zeolite with aneffective amount of at least one of a fluoro salt of chromium or afluoro salt of tin; and

(b) isolating the chromium and/or tin-containing molecular sieve productfrom the reaction mixture.

The instant process generally comprises contacting a crystalline zeolitehaving a pore diameter of at least about 3 Angstroms and having a molarSiO₂ /Al₂ O₃ ratio of at least 2, with at least 0.0075 moles of a fluorosalt of chromium or a fluoro salt of tin, per 100 grams of zeolitestarting material, said fluoro salt being in the form of a solution orslurry. The fluoro salt is preferably provided as an aqueous solution orslurry but is believed that solutions or slurries employing alcohols andother organic solvents may be employed.

It is necessary that the solution or slurry be maintained at aneffective pH. The "effective pH" is a pH such that under effectiveprocess conditions; a) a monomeric speices of the chromium and/or tin ispresent in the reaction solution; and b) the pH is high enough to avoidundue destructive acidic attack on the particular zeolite structure,apart from the intended reaction with an effective amount of the fluorosalt. The effective amount of fluoro salt is that amount which providessufficient fluoride and chromium and/or tin for the process and thedesired amount of chromium and/or tin in the final molecular sieveproduct. The effective pH value for this invention is generally greaterthan one (1), more preferably greater than 3 (three) and most preferablyin the range of about 3 to about 7 (seven).

A pH of about 3 or more usually assures that no acid degradation of thezeolite occurs but it may not necessarily be the optimum pH for theformation of monomeric species of either chromium and/or tin in thesolution. At pH values below about 3 crystal degradation of manyzeolites is found to be unduly severe. Whereas at pH values higher than7, insertion of the chromium and/or tin may be slow from a practicalstandpoint as a result of the solubility of chromium and/or tin at thesepHs and as a result of certain polymerization reactions. A pH of 7 andabove typically results in no monomeric species of either chromiumand/or tin being present in the solution so that very littlesubstitution of these metal atoms in the framework would occur.Frequently the polymeric species of chromium and/or tin will precipitateas solid oxides or hydrous oxides at pH 7 or above.

The fluoro salt solution or slurry is brought into contact with thezeolite either incrementally or continuously at a slow rate wherebyframework aluminum atoms of the zeolite are removed and replaced bychromium and/or tin atoms from the fluoro salt.

The solution or slurry of the fluoro salt, preferably aqueous, isbrought into contact with the zeolite either incrementally orcontinuously at an effective rate such that a portion of the frameworkaluminum atoms are removed and replaced by chromium and/or tin atoms ata rate which preferably retains at least 80 percent and more preferablyat least 90 percent of the crystal structure of the starting zeolite.

The fluoro salt used as the aluminum extractant and also as the sourceof chromium and/or tin, which is inserted into the zeolite structure inplace of the extracted aluminum, can be any of the fluoro salts havingthe general formula:

    A.sub.2/b MF.sub.6 or A.sub.2/b MF.sub.4

where "M" is tin and "A" is a metallic or non-metallic cation, havingthe valence "b". Cations represented by "A" include alkylammonium, H⁺,NH₄ ⁺, Mg⁺⁺, Li⁺, Na⁺, K⁺, Ba⁺⁺, Cd⁺⁺, Cu⁺, Ca⁺⁺, Cs⁺, Fe⁺⁺, Co⁺⁺, Pb⁺⁺,Mn⁺⁺, Rb⁺, Ag⁺, Sr⁺⁺, Tl⁺ and Zn⁺⁺, or the formula A_(2/b) MF₅, where"M" is chromium. The ammonium and hydronium cation forms of the fluorosalts are generally preferred because of their solubility in water andalso because these cations form water soluble by-product salts uponreaction with the zeolite, e.g., (NH₄)₃ AlF₆ and/or (NH₄)₂ AlF₅. Othersalts which may be used include a combination of salts of MF₃ and3/2(NH₄ HF₂) or MF₄ and NH₄ HF₂ where M is chromium or tin. Preferredfluoro salts are (NH₄)₃ CrF₅ ; CrF₃.3/2((NH₄)HF₂); NH₄ SnF.sub. 3 ; SnF₂.3/2(NH₄ HF₂) and SnF₄.NH₄ HF₂.

The manner in which the fluoro salt of chromium or the fluoro salt oftin and the starting zeolite are brought into contact and the overallprocess of substituting chromium and/or tin for aluminum in the zeoliteframework is believed to be a two step process in which the aluminumextraction step tends to, unless controlled, proceed very rapidly whilethe insertion of chromium and/or tin is generally relatively slow. Ifdealumination becomes too extensive without the substitution of chromiumand/or tin the crystal structure become seriously degraded andultimately collapses. While not wishing to be bound by any particulartheory, it appears that fluoride ion acts as the agent for extraction offramework aluminum in accordance with the equation: ##STR3##

It is important, therefore, that the initial dealumination step beinhibited and the step involving insertion of chromium and/or tin bepromoted to achieve the desired molecular sieve product. It is foundthat the various zeolites have varying degrees of resistance towarddegradation as a consequence of framework aluminum extraction withoutsubstitution of chromium and/or tin into the framework. Accordingly, forthe reasons stated above the pH is preferably within the range of 3 to7. The higher pH inhibits the rate and amount of dealumination. Also,increasing the reaction temperature tends to increase the rate ofsubstitution of chromium and/or tin. Increasing the reaction temperaturehas been found to have less of an effect on dealumination than the pH ofthe solution. Therefore, the pH may be considered a means of controllingdealumination while temperature may be considered as a means ofcontrolling the substitution rate.

Whether it is necessary or desirable to buffer the reaction system orselect a particular fluoro salt concentration to control the pH isreadily determined for each zeolite species by routine observation andevaluation. The question of whether the reaction system mayadvantageously be buffered will in large part depend on the selection ofthe particular starting zeolite, since zeolites have varying tolerancesto acid and base media. For example, some zeolites such as mordenite andclinoptilolite can withstand very low pH conditions and a high level ofdealumination without collapse of the crystal structure. When it isadvantageous to buffer the reaction mixture in a particular pH range thereaction mixture may be buffered in a manner as generally heretoforeemployed in the art. The use of buffering salts, such as ammoniumacetate, or use of an inert solid to react with excess acid or base,e.g. clays or aluminas, may be suitable to buffer the pH of the reactionmixture.

Theoretically, there is no lower limit for the concentration of fluorosalt of chromium and/or tin in the aqueous solution or slurry employed.A slow rate of addition of the fluoro salt generally provides adequatetime for the insertion of chromium and/or tin as a framework substitutefor extracted aluminum before excessive aluminum extraction occurs withconsequent collapse of the crystal structure. Practical commercialconsiderations, however, may require that the reaction proceed asrapidly as possible, and accordingly the conditions of reactiontemperature and reagent concentrations will necessarily be optimizedwith respect to each zeolite starting material and with respect tocommercial operation. In general it is believed that the more highlysiliceous the zeolite, the higher the permissible reaction temperatureand the lower the pH conditions which may be employed in the instantprocess. In general the preferred effective reaction temperature iswithin the range between about 10° C. and about 99° C., preferablybetween about 20° C. and 95° C., but temperatures of 125° C. or higherand as low as 0° C. are believed employable in some instances with somezeolite starting materials and with fluoro salts in a form other thanaqueous solutions or slurries. The maximum concentration of fluoro saltin the aqueous solution employed is, of course, interrelated to thetemperature and pH factors and also with the time of contact between thezeolite and the solution and the relative proportions of zeolite andfluoro salt. Solutions having fluoro salt concentrations of betweenabout 10⁻³ moles per liter of solution and up to saturation of thesolution can be employed, but it is preferred that concentrations in therange of between about 0.5 and about 1.0 moles per liter of solution beused. In addition, as hereinbefore discussed, slurries of the fluorosalts of chromium and/or tin may be employed. The aforementionedconcentration values are with respect to true solutions, and are notintended to apply to the total fluoro salts in slurries of the salts inwater. Even very slightly soluble fluoro salts can be slurries in waterand used as a reagent, the undissolved solids being readily available toreplace dissolved molecular species consumed in reaction with thezeolite. As stated hereinabove, the amount of dissolved fluoro saltsemployed with respect to the particular zeolite being treated willdepend to some extent upon the physical and chemical properties of theindividual zeolites and other effective process conditions. However, theminimum value for the amount of fluoro salt to be added is preferably atleast equivalent to the minimum mole fraction of aluminum to be removedfrom the zeolite.

In specifying the proportions of the zeolite starting material oradsorption properties of the zeolite product and the like herein, the"anhydrous state" of the zeolite will be intended unless otherwisestated. The term "anhydrous state" is employed herein to refer to amaterial substantially devoid of both physically adsorbed and chemicallyadsorbed water. In general a zeolite may be prepared in the anhydrousstate by heating the zeolite in dry air at about 450° C. for about 4hours.

It is apparent from the foregoing that, with respect to effectiveprocess conditions, it is desirable that the integrity of the zeolitecrystal structure be substantially maintained throughout the process,and that, in addition to having chromium and/or tin atoms inserted intothe lattice, the zeolite retains at least 60 percent, preferably atleast 80 and more preferably at least 90 percent of its originalcrystallinity. A convenient technique for assessing the crystallinity ofthe products relative to the crystallinity of the starting material isthe comparison of the relative intensities of the d-spacings of theirrespective X-ray powder diffraction patterns. The sum of the peakheights, in terms of arbitrary units above background, of the startingmaterial is used as the standard and is compared with the correspondingpeak heights of the products. When for example, the numerical sum of thepeak heights of the molecular sieve product is 85 percent of the valueof the sum of the peak heights of the starting zeolite, then 85 percentof the crystallinity has been retained. In practice it is common toutilize only a portion of the d-spacing peaks for this purpose, as forexample, five of the six strongest d-spacings. In zeolite Y thesed-spacings correspond to the Miller Indices 331, 440, 533, 642 and 555.Products of the instant invention will have a certain fraction of theframework tetrahedra replaced by tin and/or chromium atoms. Becauseatoms of these heavier elements are incorporated there may be a decreasein the X-ray crystallinity values due to scatter because of the heavierelements. In this case, more reliable indicia of the crystallinityretained by the zeolite product are the degree of retention of surfacearea or the degree of retention of the adsorption capacity. Surfaceareas can be determined by the well-known Brunauer-Emmett-Teller method(B-E-T). See for example, Journal of American Chemical Society, Volume60, page 309 (1938) using nitrogen as the adsorbate. In determining theadsorption capacity, the capacity for oxygen at -183° C. (90° K.) at 100Torr is preferred.

Analysis of the Substitution Mechanism

The following is a hypothetical description of the mechanism involvedand may not be the actual mechanism that is taking place. Thisdescription is based upon the present available data and analysis of thesubstitution products of this invention. This hypothetical descriptionseems to be consistent with that data and may help to explain thisunique process.

All available evidence, to date, indicates that the above describedprocess of this invention is unique is being able to produce zeolitesessentially free of defect structure and having chromium and/or tininserted into the framework by a secondary synthesis process. Inuntreated, i.e. naturally occurring or as-synthesized zeolites theoriginal tetrahedral structure is conventionally represented as ##STR4##

After treatment with a complexing agent such asethylene-diamine-tetraacetic acid (H₄ EDTA) in which a stoichiometricreaction occurs whereby framework aluminum atoms along with anassociated cation such as sodium is removed as NaAlEDTA, it ispostulated that the tetrahedral aluminum is replaced by four protonswhich form a hydroxyl "nest", as follows: ##STR5##

In the practice of this invention, a two-step process is envisioned. Inthe first step of the treatment, tetrahedral aluminum atoms are firsthydrolyzed and removed from the zeolite framework, whereupon theyimmediately react to form a more stable aluminum species or compound(i.e. aluminum fluoride species).

In the second step, ions of suitable size and coordination number areinserted into the vacant tetrahedral sites created by the dealumination.

85,902,354.1 (U.S. patent application Ser. No. 604,179), involvesreplacement of framework aluminum by either iron and/or titanium. Thepresent work involves replacement by either tin atoms or chromium atomsor both into vacant framework sites created by the dealumination.

The individual steps of the process can be accomplished in separateoperations. However, it is more desirable to perform both steps in asingle efficient operation. A particularly efficient class of compoundswhich can effect the dealumination and framework substitution steps in asingle operation can be designated by J_(x) TF_(y), where T representsthe substituting tetrahedral atom. The substituting tetrahedral atom (T)when hydrolyzed in solution forms a hydroxylated species and an acid.The acid subsequently attacks the Al in the framework to cause thedealumination. The fluoride (F) serves to complex with the removedaluminum atoms, and J is the charge-balancing cation or cations. Whilethe process is carried out in an aqueous system, it is not necessarythat the J_(x) TF_(y) compound be dissolved in the solution. It is onlynecessary that it be sufficiently soluble to initiate the reaction withthe zeolite. It is important that the reaction byproduct (the aluminumfluoride) be in a form that is readily removed from the zeolite by awashing step, subsequent to the substitution reaction. The presence offluoride in the zeolite product in concentrations as low as 1 weightpercent (or even lower), results in decreased thermal stability of thezeolite crystals. The residual fluoride can react with Si in the zeoliteat elevated temperatures to cause the zeolite crystal to collapse.

Salts of the class of compounds J_(x) TF_(y) which have been used in thepractice of this invention are:

NH₄ SnF₃ ; 3(NH₄ F).CrF₃ ; 3(NH₄ HF₂).CrF₃, SnF₂.NH₄ HF₂ ; SnF₄.NH₄ HF₂; and CrF₃.NH₄ HF₂.

Among the list of zeolites known to react with one or more of the abovelisted compounds to effect framework substitution are: the syntheticzeolite Y, mordenite, zeolite L and zeolite LZ-202 (an omega typezeolite prepared without the use of a templating agent as disclosed in(U.S. Pat. No. 3,840,779). With all of these zeolites, the reaction todealuminate the starting zeolite and replace the removed aluminum atomswith a different tetrahedral atom did take place, at least to someextent, although the resulting zeolite may not have been the optimumproduct.

The chemistry of the process can be envisioned approximately in thefollowing way. In the first step an aqueous slurry of the zeolite iscontacted with a solution of J_(x) TF_(y) salt. In some cases, becauseof the limited solubility of J_(x) TF_(y), the zeolite and the salt canbe slurried together. The salt hydrolyzes in aqueous solution to formacid, H₃ O⁺ and free fluoride. One example of this hydrolysis where T=Snand J=NH₄ can be depicted as follows:

    (NH.sub.4).sub.2 SnF.sub.6 →2(NH.sub.4).sup.+ +2F.sup.- +SnF.sub.4 a)

    SnF.sub.4 +2H.sub.2 O.sup.+ +F.sup.-                       b)

    SnF.sub.3 OH+2H.sub.2 O→SnF.sub.2 (OH).sub.2 +H.sub.3 O.sup.+ +F.sup.-                                                  c)

    SnF.sub.2 (OH).sub.2 +2H.sub.2 O→SnF(OH).sub.3 +H.sub.3 O.sup.+ +F.sup.-                                                  d)

    SnF(OH).sub.3 +2H.sub.2 O→Sn(OH).sub.4 +H.sub.3 O.sup.+ +F.sup.-e)

The acid thus formed (H₃ O)⁺, reacts rapidly to dealuminate the zeolite.The removed aluminum rapidly reacts with the free fluoride to formaluminum fluoride salts such as AlF₃, (NH₄)₂ AlF₅, and (NH₄)₃ AlF₆.

This reaction is the most crucial part of the process, since thedealumination step is very rapid. If too much dealumination occurs(without substitution into the vacant tetrahedral sites), the zeolitequickly loses its crystal structure. The use of a buffer such asammonium acetate, thereby keeping the pH greater than about 6.0, can beused to slow down the hydrolysis so that the slower substitution stepcan take place. Another method of controlling the dealumination step isto add the J_(x) TF_(y) solution very slowly to the zeolite slurry. Inthis manner, some substitution can occur before the zeolite framework isexcessively dealuminated to the point of causing crystal collapse. Withthe slow addition of the J_(x) TF_(y) solution, the zeolite itself actsas a "buffer" in the system.

The second step is the substitution of a new tetrahedral atom into thezeolite structure in place of the removed aluminum atom. This step hasbeen found to be the overall rate-limiting or slow step. Increasing thetemperature of the system increases the rate of substitution, but it mayalso speed up the rate of other undesirable side reactions such as thedealumination or the continued hydrolysis of T to form a polymericspecies which will no longer be able to substitute in the frameworkdefect sites. The exact chemistry of the substitution step is not knownin detail. It can be suggested that dealumination of the zeolite leavesa hydroxyl nest in the vacant site, which in turn reacts with thehydrolyzed form of the substituting tetrahedral atom.

The stepwise reaction can be depicted as follows: ##STR6##

THE EXPERIMENTAL CONDITIONS

The infrared spectrum of the aluminum depleted zeolite will show a broadnondescript absorption band beginning at about 3750 cm⁻¹ and extendingto about 3000 cm⁻¹. The size of this absorption band or envelopeincreases with increasing aluminum depletion of the zeolite. The reasonthat the absorption band is so broad and without any specific absorptionfrequency is that the hydroxyl groups in the vacant sites in theframework are coordinated in such a way that they interact with eachother (hydrogen bonding). The hydroxyl groups of adsorbed watermolecules are also hydrogen-bonded and produce a similar broadadsorption band as do the "nest" hydroxyls. Also, certain other zeolitichydroxyl groups, exhibiting specific characteristic absorptionfrequencies within the range of interest, will if present, causeinfrared absorption bands in these regions which are superimposed on theband attributable to the "nest" hydroxyl groups. These specifichydroxyls are created by the decomposition of ammonium cations ororganic cations present in the zeolite.

It is, however, possible to treat zeolites, prior to subjecting them toinfrared analysis, to avoid the presence of the interfering hydroxylgroups and thus be able to observe the absorption attributable to the"nest" hydroxyls only. The hydroxyls belonging to adsorbed water areavoided by subjecting the hydrated zeolite sample to vacuum activationat a moderate temperature of about 200° C. for about 1 hour. Thistreatment permits desorption and substantially complete removal of theadsorbed water. Complete removal of adsorbed water can be ascertained bynoting when the infrared absorption band at about 1640 cm⁻¹, the bendingfrequency of water molecules, has been removed from the spectrum.

The decomposable ammonium cations can be removed, at least in largepart, by ion-exchange and replaced with metal cations, preferably bysubjecting the ammonium form of the zeolite to a mild ion exchangetreatment with an aqueous NaCl solution. The OH absorption bandsproduced by the thermal decomposition of ammonium cations are therebyavoided. Accordingly the adsorption band over the range of 3745 cm⁻¹ toabout 3000 cm⁻¹ for a zeolite so treated is almost entirely attributableto hydroxyl groups associated with defect structure and the absoluteabsorbance of this band can be a measure of the degree of aluminumdepletion.

It is found, that the ion-exchange treatment, which must necessarily beexhaustive even though mild, required considerable time. Also thecombination of the ion-exchange and the vacuum calcination to removeadsorbed water does not remove every possible hydroxyl other than defecthydroxyls which can exhibit absorption in the 3745 cm⁻¹ to 3000 cm⁻¹range. For instance, a rather sharp band at 3745 cm⁻¹ has beenattributed to the Si--OH groups situated in the terminal latticepositions of the zeolite crystals and to amorphous (non-zeolitic) silicafrom which physically adsorbed water has been removed. For these reasonsit is preferred to use a somewhat different criterion to measure thedegree of defect structure in the zeolite products of this invention.

In the absence of hydrogen-bonded hydroxyl groups contributed byphysically adsorbed water, the absorption frequency least affected byabsorption due to hydroxyl groups other than those associated withframework vacancies or defect sites is at 3710±5 cm⁻¹. Thus the relativenumber of defect sites remaining in a zeolite product of this inventioncan be gauged by first removing any adsorbed water from the zeolite,determining the value of the absolute absorbance in its infraredspectrum at a frequency of 3710 cm⁻¹, and comparing that value with thecorresponding value obtained from the spectrum of a zeolite having aknown quantity of defect structure. The following specific procedure hasbeen arbitrarily selected and used to measure the amount of defectstructure in the products prepared in the Examples appearinghereinafter. Using the data obtained from this procedure it is possible,using simple mathematical calculation, to obtain a single andreproducible value hereinafter referred to as the "Defect StructureFactor", denoted hereinafter by the symbol "z", which can be used incomparing and distinguishing the present novel zeolite compositions fromtheir non-chromium and/or tin containing counter-parts.

DEFECT STRUCTURE FACTOR "Z" (A) Defect Structure Zeolite Standard

Standards with known amounts of defect structure can be prepared bytreating a crystalline zeolite of the same species as the product samplewith ethylenediaminetetraacetic acid by the standard procedure of Kerras described in U.S. Pat. No. 3,442,795. In order to prepare thestandard it is important that the starting zeolite be well crystallized,substantially pure and free from defect structure. The first two ofthese properties are readily determined by conventional X-ray analysisand the third by infrared analysis using the procedure set forth in part(B) hereof. The product of the aluminum extraction should also be wellcrystallized and substantially free from impurities. The amount ofaluminum depletion, i.e., the mole fraction of tetrahedral defectstructure of the standard samples can be ascertained by conventionalchemical analytical procedure. The molar SiO₂ /Al₂ O₃ ratio of thestarting zeolite used to prepare the standard sample in any given caseis not narrowly critical, but is preferably within about 10% of themolar SiO₂ /Al₂ O₃ ratio of the same zeolite species used as thestarting material in the practice of the process of the presentinvention.

(B) Infrared Spectrum of Product Samples and Defect Structure ZeoliteStandard

Fifteen milligrams of the hydrated zeolite to be analyzed are pressedinto a 13 mm. diameter self-supporting wafer in a KBr die under 5000lbs. pressure. The wafer is then heated at 200° C. for 1 hour at apressure of not greater than 1×10⁻⁴ mm Hg to remove all observabletraces of physically adsorbed water from the zeolite. This condition ofthe zeolite is evidenced by the total absence of an infrared absorptionband at about 1640 cm⁻¹. Thereafter, and without contact with adsorbablesubstances, particularly water vapor, the infrared spectrum of the waferis obtained on an interferometer system at 4 cm⁻¹ resolution over thefrequency range of at least 3745 to 3000 cm⁻¹. Both the product sampleand the standard sample are analyzed using the same interferometersystem to avoid discrepancies in the analysis due to differentapparatus. The spectrum, normally obtained in the transmission mode ofoperation is mathematically converted to and plotted as wave number vs.absorbance.

(C) Determination of the Defect Structure Factor

The defect structure factor (z) is calculated by substituting theappropriate data into the following formula: ##EQU1## wherein AA.sub.(ps) is the infrared absolute absorbance measured above theestimated background of the product sample at 3710 cm⁻¹ ; AA .sub.(std)is the absolute absorbance measured above the background of the standardat 3710 cm⁻¹ and the mole fraction of defects in the standard aredetermined in accordance with part (A) above.

Once the defect structure factor, z, is known, it is possible todetermine from the wet chemical analysis of the product sample for SiO₂,AlO₃, chromium and/or tin and the cation content as M_(2/n) O whetherchromium and/or tin has been substituted for aluminum in the zeolite asa result of the treatment and also the efficiency of the substitution ofchromium and/or tin.

The essential X-ray powder diffraction patterns appearing in thisspecification and referred to in the appended claims are obtained usingeither: 1) standard X-ray powder diffraction techniques; or 2) computerbased techniques using copper K-alpha radiation and using Siemens D-500X-ray powder diffractometers with Siemens Type K-805 X-ray sources,available from Siemens Corporation, Cherry Hill, N.J., with appropriatecomputer interface. When employing the standard X-ray technique theradiation source is a high-intensity, copper target, x-ray tube operatedat 50 Kv and 40 ma. The diffraction pattern from the copper K alpharadiation and graphite monochromator is suitably recorded by an X-rayspectrometer scintillation counter, pulse-height analyzer andstrip-chart recorder. Flat compressed powder samples are scanned at 2°(2 theta) per minute, using a 2 second time constant. Interplanarspacings (d) are obtained from the position of the diffraction peaksexpressed as 2 theta, where 2 theta is the Bragg angle as observed onthe strip chart. Intensities are determined from the heights ofdiffraction peaks after subtracting background.

All of the zeolite samples were evaluated according to standardanalytical procedures. The x-ray crystallinity of most samples wasmeasured using the Siemens D-500 where peak areas as well as peakintensities of all major reflections were measured and compared againstuntreated samples of the starting materials. It was expected that theproduct of a successful experiment would maintain a major fraction ofits x-ray crystallinity. Unit cell values were measured on materialspossessing cubic unit cells (a_(o)).

Framework infrared spectra of the treated zeolites were compared to theframework spectra of the respective starting materials. A generaloverall shift of the framework absorption frequencies to higher wavenumbers is a good indication of a higher silicon content in theframework. Shift of the asymmetric stretch band at about 950-1250 cm⁻¹accompanies dealumination. The symmetric stretch band, 750-835 cm⁻¹ ismore sensitive to the actual silicon content in the framework, shiftingto higher wave numbers as the silicon content increases. Very little isknown about the effect of substitution of atoms other than silicon intothe zeolite framework on the position of these bands. Very little effecton the position of the symmetric stretch band has been observed as aresult of simple dealumination. However, because there are not studiesof the effect of dealumination on the positions or shifts of theframework infrared bands with zeolites other than Y and perhapsmordenite; the lack of a substantial shift of the symmetric stretch bandwas not used as the sole criterion to judge the degree of metal atomsubstitution.

More specifically, there are no studies of the effect of substitutingeither chromium or tin or both for aluminum in the zeolite framework onshifts of framework infrared bands. A general assumption would be thations larger than Al would increase the unit cell size causing a decreasein framework infrared absorption band positions. Conversely,substitution of ions smaller than Al into the zeolite framework wouldcause a decrease in unit cell size and an increase in framework infraredabsorption band positions.

The hydroxyl region infrared spectrum was used to evaluate the relativeamount of framework defect sites in the zeolite product of thisinvention. For a more thorough description of this method of evaluationsee U.S. Pat. No. 4,503,023. Briefly, using standard procedures, theabsolute absorbance (above background) at 3710 cm⁻¹ was measured andcompared to a standard sample of aluminum-depleted NaY which contained aknown number of defects. The defect structure factor (z) of thereference standard was 0.140 and gave rise to an absolute absorbancevalue of 0.330 at 3710 cm⁻¹ of the infrared spectrum. The referencevalue of z in this case is the mole fraction of vacant tetrahedral sitesin the zeolite framework of the aluminum-depleted NaY. Fourteen percentof all of the tetrahedral sites do not contain a tetrahedral atom (Si orAl), but rather, some form of hydrogen-bonded OH groups.

In determining the cation equivalency, i.e. the molar ratio M⁺ Al ineach zeolite product, it is advantageous to perform the routing chemicalanalysis on a form of the zeolite in which "M" is an equivalentmonovalent cation other than hydrogen. This avoids the uncertainty whichcan arise in the case of divalent or polyvalent metal zeolite cations asto whether the full valence of the cation is employed in balancing thenet negative charge associated with each AlO₄ ⁻ tetrahedron.

EXAMPLES

The following examples are provided to illustrated the invention and arenot intended to be limiting thereof.

Practice of the invention is demonstrated by the following examples.After the substitution of Sn and Cr in place of Al in the framework ofzeolites via treatment with aqueous ammonium fluoride salts, all thezeolite products were washed well in hot distilled water followingreaction. Samples of the dried powders were examined by x-ray powderdiffraction techniques for retention of crystallinity. Those samplesjudged to be crystalline were further examined by differential thermalanalysis methods (DTA), measurement of O₂ adsorption isotherms at -183°C. (90° K.), measurement of H₂ O adsorption capacity at 4.6 torr and 25°C., infrared analyses of both the OH region and the mid-range(framework) region, and finally by complete chemical analysis.

In some of the X-ray patterns reported, the relative intensities of thed-spacings are indicated by the notations vs, s, m, w and vw whichrepresent very strong, strong, medium, weak and very weak, respectively.

Examples 1 through 5 disclose the substitution of Cr³⁺ in the frameworkof Zeolite Y and the resulting product was designated LZ-239.

EXAMPLE 1

Two gm NH₄ Y (anhydrous weight) containing 8.544 millimoles of Al wereslurried in 100 ml distilled water heated at 75° C. Fifty ml of a secondsolution containing 21.36 millimoles CrF₃ and 64.08 millimoles NH₄ HF₂in 250 ml distilled water, was added incrementally to the zeolite slurryat a rate of 2 ml every 5 minutes. Following the addition of chromesolution, the temperature was raised to 95° C. and the slurry wasdigested for 3 hours at 95° C. A green colored product was obtainedwhich was filtered, washed free of soluble fluoride with hot distilledwater, dried and characterized. The product contained 11 weight percentCr₂ O₃, it showed substantially reduced X-ray crystallinity, and anestimated unit cell value of 24.55Å and and a substantially increase inthe Defect Structure Factor, z. Reduced crystallinity may have beencaused by two factors in this case. A certain amount of apparentdisorder in the structure is to be expected due to the larger chromiumcation which can be present both in the framework and as a hydroxylatedcation [Cr(OH)², Cr(OH)₂ ⁺ ]. Incorporation of the heavier chromiumatoms into the structure should cause loss of peak intensity and areadue to the scattering of X-rays by the heavier atoms of chromium. Inaddition, the acidic nature of the bifluoride anion probably caused somedegradation to the acid sensitive Y zeolite framework structure.

The framework mole fractions of oxides are set forth below for thestarting NH₄ Y and the LZ-239 product.

(a) Mole fractions of oxides (TO₂):

Starting NH₄ Y: (Al₀.277 Si₀.705 ``₀.018)O₂

LZ-239 Product: (Al₀.115 Cr₀.075 Si₀.634 ``₀.176)O₂

(b) Mole Fraction of Aluminum Removed, N: 0.162

(c) Percent of Aluminum Removed, N/a×100:58

(d) Change in Defect Structure Factor, Δz:0.158

(e) Moles of Chromium Substituted per Mole of Aluminum Removed, c/N:0.463

EXAMPLE 2

Two gm NH₄ Y (anhydrous weight) containing 8.544 millimoles of Al wereslurried in 100 ml distilled water heated at 75° C. Fifty ml of a secondsolution containing 21.36 millimoles CrF₃ and 64.08 millimoles NH₄ F in250 ml distilled water, was added incrementally to the zeolite slurry ata rate of 2 ml every 5 minutes. Following the addition of the chromesolution, the temperature was raised to 95° C. and the slurry wasdigested for 3 hours at 95° C. The product was filtered, washed free ofsoluble fluoride with hot distilled water, dried and characterized. Agreen colored product which was obtained contained 10 weight percent Cr₂O₃. It showed good retention of X-ray crystallinity, and an estimatedunit cell value of 24.58 Å.

The framework mole fractions of oxides are set forth below for thestarting NH₄ Y and the LZ-239 product.

(a) Mole fractions of oxides (TO₂):

Starting NH₄ Y: (Al₀.277 Si₀.705[ ]0.018)O₂

LZ-239 Product: (Al₀.210 Cr₀.080 Si₀.660[ ]0.050)O₂

(b) Mole fraction of Aluminum Removed, N: 0.067

(c) Percent of Aluminum Removed, N/a×100: 24

(d) Change in Defect Structure Factor, Δ_(z) : 0.032.

(e) Moles of Chromium Substituted per Mole of Aluminum Removed, c/N:1.19

EXAMPLE 3

Two gm NH₄ Y (anhydrous weight) containing 8.544 millimoles of Al wereslurried in 100 ml distilled water heated at 75° C. Fifty ml of a secondsolution containing 21.36 millimoles CrF₃ and 64.08 millimoles NH₄ F in250 ml distilled water, was added incrementally to the zeolite slurry ata rate of 2 ml every 5 minutes. Following the addition of the chromesolution, the temperature was raised to 95° C. and the slurry wasdigested for half an hour. The product was filtered, washed free ofsoluble fluoride with hot distilled water, dried and characterized. Theproduct contained 10 weight percent Cr₂ O₃, showed good retention ofX-ray crystallinity, and an estimated unit cell value of 24.63 Å.

The framework mole fractions of oxides are set forth below for thestarting NH₄ Y and the LZ-239 product.

(a) Mole fractions of oxides (TO₂):

Starting NH₄ Y: (Al₀.277 Si₀.705[ ]0.018)O₂

LZ-239 Product: (Al₀.206 Cr₀.082 Si₀.665[ ]0.047)O₂

(b) Mole Fraction of Aluminum Removed, N/a: 0.071

(c) Percent of Aluminum Removed, N/a×100: 26

(d) Change in Defect Structure Factor, Δ_(z) : 0.029.

(e) Moles of chromium Substituted per Mole of Aluminum Removed, c/N:1.15.

EXAMPLE 4

Two gm NH₄ Y (anhydrous weight) containing 8.544 millimoles of Al wereslurried in 100 ml distilled water heated at 75° C. Fifty ml of a secondsolution containing 21.36 millimoles CrF₃ and 64.08 millimoles NH₄ F in250 ml distilled water, was added incrementally to the zeolite slurry ata rate of 2 ml every 5 minutes. The slurry was digested for half an hourat 75° C. The product was filtered, washed free of soluble fluoride withhot distilled water, dried and characterized. The product contained 10weight percent Cr₂ O₃, showed good retention of X-ray crystallinity, andan estimated unit cell value of 24.64 Å.

The framework mole fractions of oxides are set forth below for thestarting NH₄ Y and the LZ-239 product.

(a) Mole fractions of oxides (TO₂):

Starting NH₄ Y: (Al₀.277 Si₀.705[ ]0.018)O₂

LZ-239 Product: (Al₀.204 Cr₀.079 Si₀.658[ ]0.059)O₂

(b) Mole Fraction of Aluminum Removed, N: 0.073

(c) Percent of Aluminum Removed, N/a×100: 26

(d) Change in Defect Structure Factor, Δ_(z) : 0.041

(e) Moles of chromium Substituted per Mole of Aluminum Removed, c/N:1.08

The molecular sieves denominated herein as LZ-239 have thecharacteristic crystal structure of zeolite Y as indicated by an X-raypowder diffraction pattern having at least the d-spacings as set forthin Table A.

                  TABLE A                                                         ______________________________________                                        LZ-239 Cr.sup.3+  Substituted Zeolite Y                                       D(A)         Relative Intensity                                               ______________________________________                                        13.9-14.3    vs                                                               8.4-8.8      m                                                                7.2-7.6      m                                                                5.5-5.7      s                                                                4.6-4.8      m                                                                4.3-4.5      m                                                                3.7-3.9      s                                                                3.2-3.4      m                                                                2.7-2.9      m                                                                ______________________________________                                    

The summary of the Chemical Analyses and Product Properties of Examples1, 2, 3 and 4 are disclosed in Table B.

                                      TABLE B                                     __________________________________________________________________________    Summary of the Chemical Analyses                                              and Product Properties of Examples 1-4                                                      Starting                                                                           Example 1                                                                           Example 2                                                                           Example 3                                                                           Example 4                                              NH.sub.4 Y                                                                         (LZ-239)                                                                            (LZ-239)                                                                            (LZ-239)                                                                            (LZ-239)                                 __________________________________________________________________________    Chemical Analyses:                                                            Na.sub.2 O, wt. %                                                                           2.32 1.06  1.97  1.64  1.66                                     (NH.sub.4).sub.2 O, wt. %                                                                   9.92 2.60  6.77  6.00  5.79                                     Al.sub.2 O.sub.3, wt. %                                                                     21.78                                                                              11.47 18.62 17.05 17.38                                    Cr.sub.2 O.sub.3, wt. %                                                                     --   11.15 10.58 10.10 9.93                                     SiO.sub.2, wt. %                                                                            65.21                                                                              74.45 68.83 64.80 65.93                                    F.sub.2, wt. %                                                                              --   0.40  0.87  0.80  0.61                                     SiO.sub.2 /Al.sub.2 O.sub.3                                                                 5.08 11.01 6.27  6.45  6.53                                     SiO.sub.2 /[Al.sub.2 O.sub.3 + Cr.sub.2 O.sub.3 ]                                           5.08 6.67  4.54  4.62  4.65                                     M.sup.+ /Al   1.07 0.60  0.89  0.85  0.81                                     X-Ray Crystallinity:                                                          % by Area     100  24    57    57    57                                       % by Intensity                                                                              100  22    55    57    56                                       Unit Cell, a.sub.O in A                                                                     24.71                                                                              24.55 24.58 24.63 24.64                                    Framework Infrared:                                                           Asym. Stretch, cm.sup.-1 :                                                                  1019 1050  1029  1029  1028                                     Sym. Stretch, cm.sup.-1 :                                                                   787  799   793   793   792                                      Hydroxyl Region Infrared:                                                     Absorb. @ 3710 cm.sup.-1 :                                                                  0.042                                                                              0.415 0.117 0.111 0.139                                    Defect Factor, z:                                                                           0.018                                                                              0.176 0.050 0.047 0.059                                    McBain Absorption Values:                                                     wt. % O.sub.2 @ 100 torr                                                                    32.7 22.0  26.8  25.8  29.2                                     and 90K:                                                                      wt. % H.sub.2 O @ 4.6 torr                                                                  30.6 22.2  26.5  26.4  28.9                                     and 25° C.:                                                            __________________________________________________________________________

EXAMPLE 5

The products of Examples 2, 3 and 4 above were examined by SEM (ScanningElectron Microscopy) and EDAX analysis techniques. Using standardcoating methods, the samples were first coated by carbon and examined,then coated with gold or silver and reexamined. The carbon coatedsamples provide better surfaces for EDAX analysis. Better resolution ofthe respective peaks of the different elements are obtained withoutinterference from the large peaks due to gold or silver used to coat thesamples. The gold or silver coating makes the sample a better conductorand better resolution of the details of the crystal surface is obtained.The crystals were examined first after carbon coating to obtainelemental analysis by EDAX. The substituting element, Cr, was locatedand the relative distribution of the element throughout the crystals wasnoted. Then the sample was coated with either gold or silver and thecrystallite morphology was examined to ascertain whether there wereunusual material deposits or whether the zeolite crystals had beenaltered. A sample showing the usual crystal morphology of the respectivezeolite, with no spurious crystalline or amorphous "junk", and arelatively even distribution throughout the crystals of the substitutingion, was considered to be consistent with a conclusion that thesubstituting ion had indeed substituted into the zeolite framework. EDAXof the product of Example 2 showed that Cr was well dispersed throughoutthe zeolite crystals. Significant levels of Cr were found on crystals ofall sizes. The amount of Cr was similar throughout the individualcrystals in the sample and was no different from an EDAX area scanshowing Cr distribution throughout the entire sample. The silver coatedsample showed fairly clean crystal surfaces with no evidence of anyextraneous material deposited on or with the zeolite as a result of theSecondary Synthesis treatment.

SEM and EDAX analyses of the product of Example 3 and Example 4 areconsistent with the other properties measured on the samples showing Crsubstituting for Al in the framework of the Y zeolite. Cr substituted Yzeolite is denoted LZ-239.

EXAMPLE 6

Example 6 discloses the substitution of Cr³⁺ in the framework of zeolitemordenite and the resulting product was designated LZ-249.

Twenty-five gm (anhydrous weight) of hydronium exchanged mordeniteZeolon was used. (Zeolon is a Trademark of Norton Co., Worcester, Mass.,U.S.A.), H₃ O⁺ mordenite, containing 49.85 millimoles of Al wereslurried in 200 ml distilled water heated at 75° C. Fifty ml of a secondsolution containing 24.92 millimoles CrF₃ and 74.78 millimoles NH₄ F in50 ml distilled water, was added incrementally to the zeolite slurry ata rate of 2 ml every 4 minutes. Following the addition of the chromesolution, the temperature was raised to 95° C. and the slurry wasdigested for 3 hours at 95° C. The product was filtered. The firstfiltrate was green in color but was clear on continued washing withwater. The solid product was green and was washed free of solublefluoride with hot distilled water, dried and characterized. The productcontained 3.5 weight percent Cr₂ O₃ and showed excellent retention ofX-ray crystallinity. The molecular sieves denominated herein as LZ- 249have the characteristic crystal structure of zeolite mordenite asindicated by an X-ray powder diffraction pattern having at least thed-spacings as set forth in Table C.

                  TABLE C                                                         ______________________________________                                        LZ-249 Cr.sup.3+  Substituted Mordenite                                       D(A)         Relative Intensity                                               ______________________________________                                        13.3-13.7    m                                                                8.8-9.2      m                                                                6.4-6.6      s                                                                4.4-4.6      s                                                                3.9-4.1      s                                                                3.7-3.9      m                                                                3.4-3.6      vs                                                               3.3-3.5      s                                                                3.1-3.3      s                                                                ______________________________________                                    

The framework mole fractions of oxides are set forth below for thestarting H₃ O⁺ and the LZ-249 product.

(a) Mole fractions of oxides (TO₂):

Starting H₃ O⁺ mordenite: (Al₀.097 Si₀.715[ ]0.188)O₂

LZ-249 Product: (Al₀.083 Cr₀.026 Si₀.777[ ]0.114)O₂

(b) Mole Fraction of Aluminum Removed, N: 0.014

(c) Percent of Aluminum Removed, N/a×100: 14

(d) Change in Defect Structure Factor, Δ_(z) : -0.074

(e) Moles of Chromium Substituted per Mole of Aluminum Removed, c/N:1.86

A comparison of the Cr³⁺ substituted product, designated LZ-249, withthe starting H₃ O⁺ mordenite is shown in Table D.

                  TABLE D                                                         ______________________________________                                        Summary of the Chemical Analyses                                              and Product Properties of Examples 1-4                                                         Starting                                                                      H.sub.3 O.sup.+                                                                       Example 6                                                             mordenite                                                                             (LZ-249)                                             ______________________________________                                        Chemical Analyses:                                                            Na.sub.2 O, wt. %  0.54      0.14                                             (NH.sub.4).sub.2 O, wt. %                                                                        --        2.97                                             Al.sub.2 O.sub.3, wt. %                                                                          10.17     7.78                                             Cr.sub.2 O.sub.3, wt. %                                                                          --        3.54                                             SiO.sub.2, wt. %   88.01     85.53                                            F.sub.2, wt. %     --        0.40                                             SiO.sub.2 /Al.sub.2 O.sub.3                                                                      14.69     18.66                                            SiO.sub.2 /[Al.sub.2 O.sub.3 + Cr.sub.2 O.sub.3 ]                                                14.69     14.29                                            M.sup.+ /Al        0.09      0.89                                             X-Ray Crystallinity:                                                          % by Area          100       107                                              % by Intensity     100       114                                              Framework Infrared:                                                           Asym. Stretch, cm.sup.-1 :                                                                       1080      1080                                             Sym. Stretch, cm.sup.-1 :                                                                        788       793                                              Hydroxyl Region Infrared:                                                     Absorb. @ 3710 cm.sup.-1 :                                                                       0.442     0.269                                            Defect Factor, z:  0.188     0.114                                            McBain Absorption Values:                                                     wt. % O.sub.2 @ 100 torr                                                                         18.68     18.27                                            and 90K:                                                                      wt. % H.sub.2 O @ 4.6 torr                                                                       15.68     14.03                                            and 25° C.:                                                            wt. % neopentane @ 5.96      5.08                                             500 torr & 25° C.:                                                     wt. % SF.sub.6 @ 400 torr                                                                        10.59     8.63                                             and 25° C.                                                             ______________________________________                                    

EXAMPLE 7

Example 7 discloses the substitution of Cr³⁺ in the framework of zeoliteLZ-202 and the resulting product was designated LZ-250.

LZ-202 is an omega type zeolite, possessing structure and propertiessimilar to zeolite omega, but synthesized in an organic-free medium.Twenty five gm (anhydrous weight) of ammonium exchanged LZ-202containing 91.70 millimoles of Al were slurried in 200 ml distilledwater heated at 75° C. A second solution containing 45.85 millimolesCrF₃ and 137.55 millimoles NH₄ F in 100 ml distilled water was addedincrementally to the zeolite slurry at a rate of 5 ml every 5 minutes.Following the addition of the chrome solution, the temperature wasraised to 95° C. and the slurry was digested for 3 hours at 95° C. Theproduct was filtered. The first filtrate was green in color but wasclear on washing with water. The solid product was green and was washedfree of soluble fluoride with hot distilled water, dried andcharacterized. The product contained 8.5 weight percent Cr₂ O₃ andshowed fair retention of X-ray crystallinity. However, measurements ofthe McBain adsorption capacity showed almost complete retention of porevolume and is probably a better measure of crystallinity retention thanX-ray. Incorporation of the heavier chromium atom into the frameworkwould cause reduced intensity and area values due to scatter. Themolecular sieves denominated herein as LZ-250 have the characteristiccrystal structure of zeolite LZ-202 as indicated by an X-ray powderdiffraction pattern having at least the d-spacings as set forth in TableE.

                  TABLE E                                                         ______________________________________                                        LZ-250 Cr.sup.3+  Substituted Zeolite LZ-202                                  D(A)         Relative Intensity                                               ______________________________________                                        15.4-15.8    m                                                                8.9-9.3      vs                                                               7.6-8.0      s                                                                6.6-7.0      s                                                                5.7-6.1      s                                                                4.6-4.8      m                                                                3.7-3.9      s                                                                3.6-3.8      m                                                                3.5-3.7      m                                                                3.4-3.6      s                                                                3.05-3.25    s                                                                2.98-3.18    s                                                                2.92-3.12    m                                                                2.81-3.01    s                                                                ______________________________________                                    

A comparison of the Cr³⁺ substituted product, LZ-250, with the startingNH₄ ⁺ zeolite LZ-202 is shown in the following Table F.

                  TABLE F                                                         ______________________________________                                        Summary of the Chemical Analyses                                              and Properties of LZ-250 with the Starting                                    NH.sub.4.sup.+  zeolite LZ-202.                                                               Starting  Example 7                                                           NH.sub.4 LZ-202                                                                         (LZ-250)                                            ______________________________________                                        Chemical Analyses:                                                            Na.sub.2 O, wt. % <0.02       --                                              (NH.sub.4).sub.2 O, wt. %                                                                       8.78        7.06                                            Al.sub.2 O.sub.3, wt. %                                                                         18.70       14.98                                           Cr.sub.2 O.sub.3, wt. %                                                                         --          8.53                                            SiO.sub.2, wt. %  72.98       69.79                                           F.sub.2, wt. %    --          0.83                                            SiO.sub.2 /Al.sub.2 O.sub.3                                                                     6.62        7.91                                            SiO.sub.2 /[Al.sub.2 O.sub.3 + Cr.sub.2 O.sub.3 ]                                               6.62        5.72                                            M.sup.+ /Al       0.92        0.92                                            X-Ray Crystallinity:                                                          % by Area         100         55                                              % by Intensity    100         61                                              Framework Infrared:                                                           Asym. Stretch, cm.sup.-1 :                                                                      1038        1042                                            Sym. Stretch, cm.sup.-1 :                                                                       816         817                                             Hydroxyl Region Infrared:                                                     Absorb. @ 3710 cm.sup.-1 :                                                                      0.114       0.118                                           Defect Factor, z: 0.048       0.050                                           McBain Absorption Values:                                                     wt. % O.sub.2 @ 100 torr                                                                        18.18       18.02                                           and 90K:                                                                      wt. % H.sub.2 O @ 4.6 torr                                                                      18.48       17.02                                           and 25° C.:                                                            wt. % neopentane @                                                                              1.50        3.90                                            500 torr & 25° C.:                                                     wt. % SF.sub.6 @ 400 torr                                                                       --          3.18                                            and 25° C.                                                             ______________________________________                                    

The framework mole fractions of oxides are set forth below for thestarting NH₄ -LZ-202 and the LZ-250 product.

(a) Mole fractions of oxides (TO₂):

Starting NH₄ -LZ-202: (Al₀.221 Si₀.731[ ]0.048)O₂

LZ-250 Product: (Al₀.178 Cr₀.068 Si₀.704[ ]0.050)O₂

(b) Mole Fraction of Aluminum Removed, N: 0.043

(c) Percent of Aluminum Removed, N/a×100: 19

(d) Change in Defect Structure Factor, Δ_(z) : 0.002

(e) Moles of chromium Substituted per Mole of Aluminum Removed, c/N:1.58

EXAMPLE 8

Example 8 discloses the substitution of Cr³⁺ in the framework of zeoliteL and the resulting product was designated LZ-251.

Twenty-five gm (anhydrous weight) of ammonium exchanged zeolite L, NH⁴⁺zeolite L, containing 95.25 millimoles of Al were slurried in 200 mldistilled water heated at 75° C. 100 ml of a second solution containing47.62 millimoles CrF₃ and 142.88 millimoles NH₄ F in distilled water wasadded incrementally to the zeolite slurry at a rate of 5 ml every 5minutes. Following the addition of the chrome solution, the temperaturewas raised to 95° C. and the slurry was digested for 3 hours at 95° C.The product was filtered and washed free of soluble fluoride. All of thefiltrates were colorless. The solid product was green, contained 8.3weight percent Cr₂ O₃ and showed good retention of X-ray crystallinity.Again, measurement of the retention of adsorption capacity is a bettermeasure of the retained crystallinity of the product due to scatter ofX-rays by the heavier chromium atom. The molecular sieves denominatedherein as LZ-251 have the characteristic crystal structure of zeolite Las indicated by an X-ray powder diffraction pattern having at least thed-spacings as set forth in Table G.

                  TABLE G                                                         ______________________________________                                        LZ-251 Cr.sup.3+  Substituted Zeolite L                                       D(A)         Relative Intensity                                               ______________________________________                                        15.6-16.0    vs                                                               5.9-6.1      s                                                                5.7-5.9      m                                                                4.5-4.7      s                                                                4.3-4.5      m                                                                4.2-4.4      m                                                                3.8-4.0      m                                                                3.56-3.76    m                                                                3.38-3.58    m                                                                3.18-3.38    m                                                                3.08-3.28    s                                                                2.97-3.17    m                                                                2.81-3.01    m                                                                ______________________________________                                    

The framework mole fractions of oxides are set forth below for thestarting NH₄ L and the LZ-251 product.

(a) Mole fractions of oxides (TO₂):

Starting NH₄ L: (Al₀.248 Si₀.732[ ]0.020) O₂

LZ-251 Product: (Al₀.194 Cr₀.069 Si₀.690[ ]0.047)O₂

(d) Mole Fraction of Aluminum Removed, N: 0.054

(c) Percent of Aluminum Removed, N/a×100: 22

(d) Change in Defect Structure Factor, Δ_(z) : 0.027

(e) Moles of chromium Substituted per Mole of Aluminum Removed, c/N:1.28

A comparison of the Cr³⁺ substituted product, LZ-251, with the startingNH₄ ⁺ zeolite L is shown in the following Table H.

                  TABLE H                                                         ______________________________________                                        Summary of the Chemical Analyses and Properties                               of LZ-251 with the Starting NH.sub.4 zeolite L                                                 Starting                                                                             Example 8                                                              NH.sub.4 L                                                                           (LZ-251)                                              ______________________________________                                        Chemical Analyses:                                                            K.sub.2 O, wt. %   3.51     2.98                                              (NH.sub.4).sub.2 O, wt. %                                                                        7.89     5.71                                              Al.sub.2 O.sub.3, wt. %                                                                          19.42    15.71                                             Cr.sub.2 O.sub.3, wt. %                                                                          --       8.33                                              SiO.sub.2, wt. %   67.80    65.83                                             F.sub.2, wt. %     --       0.89                                              SiO.sub.2 /Al.sub.2 O.sub.3                                                                      5.92     7.11                                              SiO.sub.2 /[Al.sub.2 O.sub.3 + Cr.sub.2 O.sub.3 ]                                                5.92     5.24                                              M.sup.+ /Al        1.00     0.92                                              X-Ray Crystallinity:                                                          % by Area          100      64                                                % by Intensity     100      64                                                Framework Infrared:                                                           Asym. Stretch, cm.sup.-1 :                                                                       1028     1031                                              Sym. Stretch, cm.sup.-1 :                                                                        768      772                                               Hydroxyl Region Infrared:                                                     Absorb. @ 3710 cm.sup.-1 :                                                                       0.048    0.111                                             Defect Factor, z:  0.020    0.047                                             McBain Absorption Values:                                                     wt. % O.sub.2 @ 100 torr                                                                         16.14    15.78                                             and 90K:                                                                      wt. % H.sub.2 O @ 4.6 torr                                                                       17.97    17.16                                             and 25° C.:                                                            wt. % neopentane @ --       8.41                                              500 torr & 25° C.:                                                     wt. % SF.sub.6 @ 400 torr                                                                        --       --                                                and 25° C.                                                             ______________________________________                                    

EXAMPLE 9

Example 9 discloses the substitution of Sn²⁺ in the framework of zeoliteY and the resulting product was designated LZ-238.

Two gm NH₄ ⁺ zeolite Y (anhydrous weight) containing 8.544 millimoles ofAl were slurried in 100 ml distilled water heated at 75° C. Fifty fiveml of a second solution containing 4.27 millimoles NH₄ SnF₃ in distilledwater was added incrementally to the zeolite slurry at a rate of 5 mlevery 5 minutes. Following addition of the fluorostannate solution, theslurry was digested for 3 hours at 95° C. The solid product wasfiltered, washed free of soluble fluoride, dried and characterized. TheLZ-238 product was yellow and contained 22.7 weight percent SnO asdetermined by chemical analysis. Based on the total characterization ofthe product, it is believed that a large fraction of the tin hasreplaced aluminum in the zeolite framework. The remainder of the tin ispresent both as cation and as a precipitated oxide, SnO. The X-raypowder pattern showed a trace of SnO in the background of the patternand a substantial reduction in the X-ray crystallinity of the Y zeolite.However, McBain adsorption capacities measured on the product show thatat least 80 percent of the void volume of the LZ-238 was retained. Thereduced X-ray crystallinity may be due to scatter caused byincorporation of the heavier tin atom into the structure of the zeolite.The molecular sieves denominated herein as LZ-238 have thecharacteristic crystal structure of zeolite Y as indicated by an X-raypowder diffraction pattern having at least the d-spacings as set forthin Table I.

                  TABLE I                                                         ______________________________________                                        LZ-238 Sn.sup.2+  Substituted Zeolite Y                                       D(A)         Relative Intensity                                               ______________________________________                                        13.9-14.3    vs                                                               8.4-8.8      m                                                                7.2-7.6      m                                                                5.5-5.7      s                                                                4.6-4.8      m                                                                4.3-4.5      m                                                                3.7-3.9      s                                                                3.2-3.4      m                                                                2.7-2.9      m                                                                ______________________________________                                    

A comparison of the Sn²⁺ substituted product, LZ-238, with the startingNH₄ ⁺ zeolite Y is shown in the following Table J.

                  TABLE H                                                         ______________________________________                                        Summary of the Chemical Analyses and Properties                               of LZ-238 with the Starting NH.sub.4.sup.+  zeolite Y                                          Starting                                                                             Example 9                                                              NH.sub.4 Y                                                                           (LZ-238)                                              ______________________________________                                        Chemical Analyses:                                                            Na.sub.2 O, wt. %  2.32     1.78                                              (NH.sub.4).sub.2 O, wt. %                                                                        9.92     4.99                                              Al.sub.2 O.sub.3, wt. %                                                                          21.78    14.96                                             Sn.sub.2 O.sub.3, wt. %                                                                          --       22.68                                             SiO.sub.2, wt. %   65.21    53.56                                             F.sub.2, wt. %     --       0.07                                              SiO.sub.2 /Al.sub.2 O.sub.3                                                                      5.08     6.07                                              SiO.sub.2 /[Al.sub.2 O.sub.3 + SnO/2]                                                            5.08     3.86                                              M.sup.+ /Al; (Na.sup.+, NH.sub.4.sup.+):                                                         1.07     0.85                                              X-Ray Crystallinity:                                                          % by Area          100      30                                                % by Intensity     100      29                                                Unit Cell, a.sub.0 in A:                                                                         24.71    24.54                                             Framework Infrared:                                                           Asym. Stretch, cm.sup.-1 :                                                                       1019     1027                                              Sym. Stretch, cm.sup.-1 :                                                                        787      792                                               Hydroxyl Region Infrared:                                                     Absorb. @ 3710 cm.sup.-1 :                                                                       0.042    0.123                                             Defect Factor, z:  0.018    0.052                                             McBain Absorption Values:                                                     wt. % O.sub.2 @ 100 torr                                                                         32.70    23.54                                             and 90K:                                                                      wt. % H.sub.2 O @ 4.6 torr                                                                       30.60    24.48                                             and 25° C.:                                                            wt. % neopentane @ --       --                                                500 torr & 25° C.:                                                     wt. % SF.sub.6 @ 400 torr                                                                        --       --                                                and 25° C.                                                             ______________________________________                                         *Sample contained some fraction of the Sn as SnO as observed in the Xray      powder pattern.                                                          

The framework mole fractions of oxides are set forth below for thestarting NH₄ Y and the LZ-238 product.

(a) Mole fractions of oxides (TO₂):

Starting NH₄ Y: (Al₀.277 Si₀.705[ ]0.018)O₂

LZ-238 Product: (Al₀.206 Sn₀.118 Si₀.624[ ]0.052)O₂

(b) Mole Fraction of Aluminum Removed, N: 0.071

(c) Percent of Aluminum Removed, N/a×100: 26

(d) Change in Defect Structure Factor, Δ_(z) : 0.034

(e) Moles of chromium Substituted per Mole of Aluminum Removed, c/N:1.66

EXAMPLE 10

Example 10 discloses the substitution of Sn²⁺ in the framework ofzeolite mordenite and the resulting product was designated LZ-252.

Twenty-five gm (anhydrous weight) of hydronium exchanged mordeniteZeolon was used. (Zeolon is a Trademark of Norton Co., Worcester, Mass.,U.S.A.), H₃ O⁺ mordenite, containing 49.85 millimoles of Al wereslurried in 200 ml distilled water heated at 75° C. A second solutioncontaining 24.92 millimoles NH₄ SnF₃ in 100 distilled water was addedincrementally to the zeolite slurry at a rate of 5 ml every 5 minutes.Following the addition of the tin solution, the temperature was raisedto 95° C. and the slurry was digested for 3 hours at 95° C. The productwas filtered, washed free of soluble fluoride with hot distilled water,dried and characterized. The product was colorless, contained 12.3weight percent SnO and showed good retention of X-ray crystallinity. Nocrystalline SnO was detected in the background of the X-ray powderpattern. The SEM and EDAX analyses of this sample show that tin is welldispersed throughout the zeolite crystals. The molecular sievesdenominated herein as LZ-252 have the characteristic crystal structureof zeolite mordenite as indicated by an X-ray powder diffraction patternhaving at least the d-spacings as set forth in Table K.

                  TABLE K                                                         ______________________________________                                        LZ-252 Sn.sup.2+  Substituted Mordenite                                       D(A)         Relative Intensity                                               ______________________________________                                        13.3-13.7    s                                                                8.8-9.2      vs                                                               6.4-6.6      s                                                                4.4-4.6      s                                                                3.9-4.1      s                                                                3.7-3.9      m                                                                3.4-3.6      vs                                                               3.3-3.5      s                                                                3.1-3.3      s                                                                ______________________________________                                    

The framework mole fractions of oxides are set forth below for thestarting H₃ O⁺ mordenite and the LZ-252 product.

(a) Mole fractions of oxides (TO₂):

Starting H₃ O⁺ mordenite: (Al₀.097 Si₀.715[ ]0.088)O₂

LZ-252 Product: (Al₀.058 Sn₀.052 Si₀.764[ ]0.126)O₂

(b) Mole Fraction of Aluminum Removed, N:0.039

(c) Percent of Aluminum Removed, N/a×100: 40

(d) Change in Defect Structure Factor, Δ_(z) : -0.062

(e) Moles of chromium substituted per mole of aluminum Removed, c/N:1.33

A comparison of the Sn²⁺ substituted product, LZ-252, with the startingH₃ O⁺ mordenite, is shown in the following Table L.

                  TABLE L                                                         ______________________________________                                        Summary of the Chemical Analyses and Properties                               of LZ-252 with the Starting H.sub.3 O.sup.+  mordenite.                                        Starting                                                                      H.sub.3 O.sup.+                                                                       Example 10                                                            mordenite                                                                             (LZ-252)                                             ______________________________________                                        Chemical Analyses:                                                            Na.sub.2 O, wt. %  0.54      --                                               (NH.sub.4).sub.2 O, wt. %                                                                        --        2.03                                             Al.sub.2 O.sub.3, wt. %                                                                          10.17     5.18                                             SnO, wt. %         --        12.27                                            SiO.sub.2, wt. %   88.01     80.29                                            F.sub.2, wt. %     --        0.10                                             SiO.sub.2 /Al.sub.2 O.sub.3                                                                      14.69     26.31                                            SiO.sub.2 /[Al.sub.2 O.sub.3 + SnO/2]                                                            14.69     13.87                                            M.sup.+ /Al        0.09      0.77                                             X-Ray Crystallinity:                                                          % by Area          100       65                                               % by Intensity     100       65                                               Framework Infrared:                                                           Asym. Stretch, cm.sup.-1 :                                                                       1080      1082                                             Sym. Stretch, cm.sup.-1 :                                                                        788       804                                              Hydroxyl Region Infrared:                                                     Absorb. @ 3710 cm.sup.-1 :                                                                       0.442     0.298                                            Defect Factor, z:  0.188     0.126                                            McBain Absorption Values:                                                     wt. % O.sub.2 @ 100 torr                                                                         18.68     14.99                                            and 90K:                                                                      wt. % H.sub. 2 O @ 4.6 torr                                                                      15.68     11.29                                            and 25° C.:                                                            wt. % neopentane @ 5.96      1.43                                             500 torr & 25° C.:                                                     wt. % SF.sub.6 @ 400 torr                                                                        10.59     3.63                                             and 25° C.                                                             ______________________________________                                    

EXAMPLE 11

Example 11 discloses the substitution of Sn²⁺ in the framework ofzeolite LZ-202 and the resulting product was designated LZ-253.

LZ-202 is an omega type zeolite, possessing structure and propertiessimilar to zeolite omega, but synthesized in an organic-free medium.Twenty-five gm (anhydrous weight) of ammonium exchanged LZ-202containing 91.70 millimoles of Al were slurried in 200 ml distilledwater heated at 75° C. A second solution containing 45.85 millimoles NH₄SnF₃ in 100 ml distilled water was added incrementally to the zeoliteslurry at a rate of 5 ml every 5 minutes. Following the addition of thetin solution, the temperature was raised to 95° C. and the slurry wasdigested for 3 hours at 95° C. The product was filtered, washed free ofsoluble fluoride with hot distilled water, dried and characterized. Theproduct contained 15.6 weight percent SnO and showed reduced X-raycrystallinity. McBain adsorption values indicate retention of at least90 percent of the void volume showing that the reduced X-raycrystallinity is probably due to scatter caused by incorporation of theheavier tin atom into the frame work structure of the zeolite. SEM andEDAX analyses were conducted and are reported in Example 13. Themolecular sieves denominated herein as LZ-253 have the characteristiccrystal structure of zeolit LZ-202 as indicated by an X-ray powderdiffraction pattern having at least the d-spacings as set forth in TableM.

                  TABLE M                                                         ______________________________________                                        LZ-252 Sn.sup.2+  Substituted Zeolite LZ-202                                  D(A)         Relative Intensity                                               ______________________________________                                        15.4-15.8    m                                                                8.9-9.3      vs                                                               7.6-8.0      s                                                                6.6-7.0      s                                                                5.7-6.1      s                                                                4.6-4.8      m                                                                3.7-3.9      s                                                                3.6-3.8      s                                                                3.5-3.7      m                                                                3.4-3.6      s                                                                3.05-3.25    s                                                                2.98-3.18    s                                                                2.92-3.12    m                                                                2.81-3.01    s                                                                ______________________________________                                    

A comparison of the Sn²⁺ substituted product, zeolite LZ-253, with thestarting NH₄ ⁺ zeolite LZ-202 is shown in the following Table N.

                  TABLE N                                                         ______________________________________                                        Summary of the Chemical Analyses and Properties                               of LZ-253 with the Starting NH.sub.4 zeolite LZ-202.                                          Starting  Example 11                                                          NH.sub.4 -LZ-202                                                                        (LZ-253)                                            ______________________________________                                        Chemical Analyses:                                                            Na.sub.2 O, wt. % <0.02       --                                              (NH.sub.4).sub.2 O, wt. %                                                                       8.78        6.67                                            Al.sub.2 O.sub.3, wt. %                                                                         18.70       13.66                                           SnO, wt. %        --          15.63                                           SiO.sub.2, wt. %  72.98       62.51                                           F.sub.2, wt. %    --          0.11                                            SiO.sub.2 /Al.sub.2 O.sub.3                                                                     6.62        7.77                                            SiO.sub.2 /[Al.sub.2 O.sub.3 + SnO/2]                                                           6.62        5.42                                            M.sup.+ /Al       0.92        0.96                                            X-Ray Crystallinity:                                                          % by Area         100         41                                              % by Intensity    100         41                                              Framework Infrared:                                                           Asym. Stretch, cm.sup.-1 :                                                                      1038        1042                                            Sym. Stretch, cm.sup.-1 :                                                                       816         815                                             Hydroxyl Region Infrared:                                                     Absorb. @ 3710 cm.sup.-1 :                                                                      0.114       0.133                                           Defect Factor, z: 0.048       0.056                                           McBain Absorption Values:                                                     wt. % O.sub.2 @ 100 torr                                                                        18.18       15.99                                           and 90K:                                                                      wt. % H.sub.2 O @ 4.6 torr                                                                      18.48       16.40                                           and 25° C.:                                                            wt. % neopentane @                                                                              1.50        1.40                                            500 torr & 25° C.:                                                     wt. % SF.sub.6 @ 400 torr                                                                       --          --                                              and 25° C.                                                             ______________________________________                                    

The framework mole fractions of oxides are set forth below for thestarting NH₄ -LZ-202 and the LZ-253 product.

(a) Mole fractions of oxides (TO₂):

Starting NH₄ -LZ-202: (Al₀.221 Si₀.731[ ]0.048)O₂

LZ-253 Product: (Al₀.177 Sn₀.077 Si₀.690[ ]0.056)O₂

(b) Mole Fraction of Aluminum Removed, N: 0.044

(c) Percent of Aluminum Removed, N/a×100: 20

(d) Change in Defect Structure Factor, Δ_(z) : -0.008

(e) Moles of chromium Substituted per Mole of Aluminum Removed, c/N:1.75

EXAMPLE 12

Example 12 discloses the substitution of Sn²⁺ in the framework ofzeolite L and the resulting product was designated LZ-254.

Twenty-five gm (anhydrous weight) of ammonium exchanged zeolite L, NH₄ ⁺zeolite L, containing 95.25 millimoles of Al were slurried in 200 mldistilled water heated at 75° C. 90 ml of a second solution containing47.62 millimoles NH₄ SnF₃ in distilled water was added incrementally tothe zeolite slurry at a rate of 5 ml every 5 minutes. Following theaddition of the tin solution, the temperature was raised to 95° C. andthe slurry was digested for 3 hours at 95° C. The product was filteredand washed free of soluble fluoride. All of the filtrates werecolorless. The solid product was yellow, contained 13.9 weight percentSnO and showed fair retention of X-ray crystallinity and excellentretention of McBain adsorption capacities. The molecular sievesdenominated herein as LZ-254 have the characteristics crystal structureof zeolite L as indicated by an X-ray powder diffraction pattern havingat least the d-spacings as set forth in Table O.

                  TABLE O                                                         ______________________________________                                        LZ-254 Sn.sup.2+  Substituted Zeolite L                                       D(A)         Relative Intensity                                               ______________________________________                                        15.6-16.0    vs                                                               5.9-6.1      s                                                                5.7-5.9      m                                                                4.5-4.7      s                                                                4.3-4.5      m                                                                4.2-4.4      m                                                                3.8-4.0      s                                                                3.56-3.76    s                                                                3.38-3.58    s                                                                3.18-3.38    m                                                                3.08-3.28    s                                                                2.97-3.17    s                                                                2.81-3.01    s                                                                ______________________________________                                    

The framework mole fractions of oxides are set forth below for thestarting NH₄ L and the LZ-254 product.

(a) Mole fractions of oxides (TO₂):

Starting NH₄ L: (Al₀.248 Si₀.732[ ]0.020)O₂

LZ-254 Product: (Al₀.210 Sn₀.072 Si₀.685[ ]0.033)O₂

(b) Mole Fraction of Aluminum Removed, N: 0.038

(c) Percent of Aluminum Removed, N/a×100: 15

(d) Change in Defect Structure Factor, Δ_(z) : 0.013

(e) Moles of chromium Substituted per Mole of Aluminum Removed, c/N: 189

A comparison of the Sn²⁺ substituted product, LZ-254, with the startingNH₄ ⁺ zeolite L is shown in the following Table P.

                  TABLE P                                                         ______________________________________                                        Summary of the Chemical Analyses and Properties                               of LZ-254 with the Starting NH.sub.4.sup.+  zeolite LZ.                                        Starting                                                                             Example 12                                                             NH.sub.4.sup.+  L                                                                    (LZ-254)                                              ______________________________________                                        Chemical Analyses:                                                            K.sub.2 O, wt. %   3.51     2.72                                              (NH.sub.4).sub.2 O, wt. %                                                                        7.89     6.09                                              Al.sub.2 O.sub.3, wt. %                                                                          19.42    15.54                                             SnO, wt. %         --       13.91                                             SiO.sub.2, wt. %   67.80    59.67                                             F.sub.2, wt. %     --       0.08                                              SiO.sub.2 /Al.sub.2 O.sub.3                                                                      5.92     6.52                                              SiO.sub.2 /[Al.sub.2 O.sub.3 + SnO/2]                                                            5.92     4.87                                              M.sup.+ /Al        1.00     0.93                                              X-Ray Crystallinity:                                                          % by Area          100      48                                                % by Intensity     100      49                                                Framework Infrared:                                                           Asym. Stretch, cm.sup.-1 :                                                                       1028     1029                                              Sym. Stretch, cm.sup.-1 :                                                                        768      770                                               Hydroxyl Region Infrared:                                                     Absorb. @ 3710 cm.sup.-1 :                                                                       0.048    0.078                                             Defect Factor, z:  0.020    0.033                                             McBain Absorption Values:                                                     wt. % O.sub.2 @ 100 torr                                                                         16.14    15.64                                             and 90K:                                                                      wt. % H.sub.2 O @ 4.6 torr                                                                       17.97    15.15                                             and 25° C.:                                                            wt. % neopentane @ --       4.21                                              500 torr & 25° C.:                                                     wt. % SF.sub.6 @ 400 torr                                                                        --       --                                                and 25° C.                                                             ______________________________________                                    

EXAMPLE 13

The products of Example 10 (Sn²⁺ substituted mordenite) and of Example11 (Sn²⁺ substituted zeolite LZ-202) were examined by Scanning ElectronMicroscopy and EDAX techniques. The LZ-252, Sn substituted mordenite,samples were examined with only carbon coating. The SEM analyses clearlyshow clean crystals with mordenite morphology. There is no evidence ofany other phase present with the zeolite that could be construed as SnOor other tin containing material. EDAX analyses were conducted on theentire area and on a spot on a zeolite crystal. The similarity betweenthe EDAX area scan and spot probe analyses indicate that the Sn isequally distributed over the entire zeolite and not found in isolatedareas of the zeolite. Since the X-ray powder patterns did not show thepresence of any extraneous crystalline phase, the SEM and EDAX are takenas supportive evidence for substitution of Sn for Al in the zeoliteframework of mordenite. Further, the analytical evaluations derived fromthe EDAX analyses, which are compared to the chemical analysis of theelements in the product in the following Table, confirm the evendistribution of the tin over the entire sample.

                  TABLE Q                                                         ______________________________________                                                Chemical EDAX      EDAX                                                       Analysis Area Scan Spot Probe*                                        ______________________________________                                        Wt. % Al: 5.37       5.1       5.6                                            Wt. % Si: 73.47      74.2      70.8                                           Wt. % Sn: 21.17      20.7      23.7                                           ______________________________________                                         *Average of (4) spots on (4) separate crystals.                          

SEM and EDAX analyses of the LZ-253, Sn substituted NH₄ ⁺ zeolite LZ-202samples were also conducted. The crystals were observed to be clean andfree of any debris. The crystal morphology had the appearance of theuntreated NH₄ ⁺ zeolite LZ-202. There was no apparent crystaldegradation. A typical spot probe analysis of the crystals showed theexpected level of tin in the sample. An EDAX area scan covering anentire clump of crystals showed the expected tin levels. These crystalsare most probably SnO, since the X-ray powder pattern had shown a traceamount of SnO in the background. The SEM and EDAX evidence is quiteclear in differentiating the precipitated SnO from the LZ-253 and showsthe presence of Sn in the zeolite crystals.

EXAMPLE 14

The products of Examples 6, 7, 10 and 11 were tested for n-butanecracking activity as hereinafter described and found to be activecatalysts. The reactor was a cylindrical quartz tube 254 mm in lengthand 10.3 mm I.D. In each test the reactor was loaded with particles ofthe test product which were 20-40 mesh (U.S. std.) in size and in anamount of from 0.5.5 grams. The products were activated in-situ in thereactor for one hour in a stream of either flowing helium or flowing airat the temperature indicated in the following tables. The reactionfeedstock was a helium-n-butane mixture containing 2 mole percentn-butane and was passed through the reactor at a rate of 50 cc/minutewith the reactor temperature maintained at 500° C. Analysis of thefeedstock and the reactor effluent was carried out using conventionalgas chromatography techniques. The reactor effluent was analyzed after10 minutes of on-stream operation. From the analytical data thepseudo-first-order rate constant (kA) was calculated. The results ofthose tests are shown in Tables R and S.

                  TABLE R                                                         ______________________________________                                                                 Consumption                                                 Ex.    Activation of n-butane                                                                            % i-butane                                  Product                                                                              No.    Temp. (°C.)                                                                       (%)      in product                                                                            KA*                                 ______________________________________                                        H.sub.3 O.sup.+                                                                      --     500, Helium                                                                              84.2     2.2     81                                  Zeolon --     600, Air   76.0     2.0     107                                 LZ-249 6      500, Helium                                                                              86.3     2.0     56                                  (Cr)   6      600, Air   49.2     3.8     39                                  LZ-252 10     500, Helium                                                                              40.1     1.9     14                                  (Sn)   10     600, Air   29.1     3.8     19                                  ______________________________________                                         *The lower the value for kA the lower the activity                       

                  TABLE S                                                         ______________________________________                                                                 Consumption                                                 Ex.    Activation of n-butane                                                                            % i-butane                                  Product                                                                              No.    Temp. (°C.)                                                                       (%)      in product                                                                            KA*                                 ______________________________________                                        NH.sub.4.sup.+                                                                       --     500, Helium                                                                              76.8     3.5     57                                  LZ-202 --     500, Air   82.1     4.1     71                                  LZ-250 7      500, Helium                                                                              93.8     1.2     40                                  (Cr)   7      500, Air   33.9     5.3     24                                  LZ-253 11     500, Helium                                                                              47.1     2.3     14                                  (Sn)   11     500, Air   74.5     2.7     52                                  ______________________________________                                         *The lower the value for kA the lower the activity                       

EXAMPLE 15

The products of Examples 3, 8, 9 and 12 were tested for n-butanecracking activity as described in Example 14 and found to be activecatalysts. The results of those tests are shown in Tables T and U.

                  TABLE T                                                         ______________________________________                                                                 Consumption                                                 Ex.    Activation of n-butane                                                                            % i-butane                                  Product                                                                              No.    Temp. (°C.)                                                                       (%)      in product                                                                            KA*                                 ______________________________________                                        NH.sub.4.sup.+                                                                       --     500, Helium                                                                              --       --      2                                   Zeolite Y                                                                            --     600, Air   --       6.6     1                                   LZ-239 3      500, Helium                                                                              33.6     4.5     24                                  (Cr)   3      500, Air   11.5     --      6                                   LZ-238 9      500, Helium                                                                              10.8     1.2     7                                   (Sn)   9      500, Air   13.2     1.1     7                                   ______________________________________                                         *The lower the value for kA the lower the activity                       

                  TABLE U                                                         ______________________________________                                                                 Consumption                                                 Ex.    Activation of n-butane                                                                            % i-butane                                  Product                                                                              No.    Temp. (°C.)                                                                       (%)      in product                                                                            KA*                                 ______________________________________                                        NH.sub.4.sup.+                                                                       --     500, Helium                                                                              --       6.5     3.4                                 Zeolite L                                                                            --     500, Air   --       6.7     4.6                                 LZ-251 8      500, Helium                                                                              12.7     5.6     8.1                                 (Cr)                                                                          LZ-254 12     500, Helium                                                                              36.4     9.4     25.0                                (Sn)                                                                          ______________________________________                                         *The lower the value for kA the lower the activity                       

EXAMPLE 16

Twenty five gm. H₃ O⁺ mordenite, containing 0.0249 moles Al₂ O₃, wasslurried in 250 ml distilled water and heated at 75° C. A 100 ml.solution containing 0.0499 moles of NH₄ SnF in water was added in 5 ml.increments every 5 minutes. The amount of Sn⁺² added was sufficient toremove and replace 100% of the framework aluminum in the zeolite. Theinitial pH of the H₃ O⁺ mordenite was 4.11, which dropped to 3.56 duringthe addition of the NH₄ SnF₃ solution, and was 3.59 at the end of theaddition. Following the addition, the slurry was digested at 95° C. for3 hours, filtered and washed free of soluble aluminum species andfluoride. The pH at the end of the digestion was 3.68. The resultingproduct was colorless and contained 12.28 wt. % SnO; the SiO₂ /Al₂ O₃was 26.3, (the starting ratio of the H₃ O⁺ mordenite was 14.7). Theproduct properties are compared to the starting H₃ O⁺ mordenite in thefollowing Table V:

                  TABLE V                                                         ______________________________________                                                       Starting    LZ-252                                                            H.sub.3 O.sup.+  mordenite                                                                Product                                            ______________________________________                                        SiO.sub.2 /Al.sub.2 O.sub.3 :                                                                  14.69         26.31                                          Cation Equivalent, M.sup.+ /Al:                                                                0.09          0.77                                           Cation Equivalent,                                                                             0.09          0.27                                           M.sup.+ /(Al + 2Sn):                                                          wt. % Sn.sup.2+  as SnO:                                                                       0             12.28                                          wt. % fluoride:  0             0.11                                           X-ray Crystallinity, %:                                                                        100           65                                             Asym. Stretch, cm.sup.-1 :                                                                     1080          1080                                           Sym. Stretch, cm.sup.-1 :                                                                      798           804                                            McBain O.sub.2, wt. %:                                                                         19.0          15.0                                           McBain H.sub.2 O, wt. %:                                                                       14.8          11.3                                           McBain neopentane, wt. %:                                                                      4.4           1.4                                            McBain SF.sub.6, wt. %:                                                                        9.1           3.6                                            ______________________________________                                    

The data in the above Table indicate that Sn⁺² has substituted into thezeolite framework, but there has been some loss in crystallinity asevidenced by the reduced adsorption capacities. Two samples of the Sn⁺²substituted sample described above were treated in the following manner.One sample was treated in 3.5M NaCl solution at 75° C. for two hours,filtered, washed and analyzed. The second ample was placed into 3.5MNaCl solution and titrated to pH 10 with 0.1N NaOH solution, filtered,washed and analyzed. The chemical analysis data for the two samples areshown below:

    ______________________________________                                                          NaCl    Titrated with                                                         Treated NaOH                                                ______________________________________                                        SiO.sub.2 /Al.sub.2 O.sub.3 :                                                                     23.87     24.96                                           Cation Equivalent, M.sup.+ /Al:                                                                   1.62      1.64                                            Cation Equivalent, M.sup.+ /(Al + 2Sn):                                                           0.76      0.58                                            ______________________________________                                    

Ion exchange of the Sn⁺² substituted mordenite shows a substantialexcess in cations relative to the amount of aluminum contained in theframework. This indicates that an additional species in the framework isnegatively charged, thus requiring a cation. The only probable speciesis Sn⁺² in the framework.

EXAMPLE 17

Fifty gm. H₃ O⁺ mordenite, containing 0.0457 moles Al₂ O₃, was slurriedin 500 ml distilled water and heated at 75° C. A 200 ml. solutioncontaining 0.0913 moles of SnF₂ and 0.0913 moles NH₄ HF₂ in water wasadded continuously at a rate of 2 ml. per minute. The amount of Sn⁺²added was sufficient to remove and replace 100% of the frameworkaluminum in the zeolite. The initial pH of the H₃ O⁺ mordenite was 1.84,which increased to 2.77 at the end of the addition of the SnF₂ solution.Following the addition, the slurry was digested at 95° C. for 3 hours,filtered and water free of soluble aluminum species and fluoride. The pHat the end of the digestion was 2.66. The resulting product wascolorless and contained 6.39 wt. % SnO; the SiO₂ /A₂ O₃ was 30.9, (thestarting ratio of the H₃ O⁺ mordenite was 16.4). The product propertiesare compared to the starting H₃ O⁺ mordenite in the following Table W:

                  TABLE W                                                         ______________________________________                                                       Starting    LZ-252                                                            H.sub.3 O.sup.+  mordenite                                                                Product                                            ______________________________________                                        SiO.sub.2 /Al.sub.2 O.sub.3 :                                                                  16.45         30.93                                          Cation Equivalent, M.sup.+ /Al:                                                                0.08          0.73                                           Cation Equivalent,                                                                             0.08          0.46                                           M.sup.+ /(Al + 2Sn):                                                          wt. % Sn.sup.+2 as SnO:                                                                        0             6.39                                           wt. % fluoride:  0             0.07                                           X-ray Crystallinity, %:                                                                        100           88                                             Asym. Stretch, cm.sup.-1 :                                                                     1082          1094                                           Sym. Stretch, cm.sup.-1 :                                                                      797           810                                            Absorbance at 3710 cm.sup.-1 :                                                                 0.403         0.218                                          "z" value:       0.171         0.093                                          McBain O.sub.2, wt. %:                                                                         19.6          16.4                                           McBain H.sub.2 O, wt. %:                                                                       15.2          10.1                                           McBain neopentane, wt. %:                                                                      5.2           1.2                                            McBain SF.sub.6, wt. %:                                                                        11.4          0.6                                            ______________________________________                                    

The data in the above Table indicate that Sn⁺² has substituted into thezeolite framework, but there has been some apparent loss incrystallinity as evidenced by the reduced adsorption capacities.However, the X-ray crystallinity value for the substituted productremains high and the amount of defects in the structure are reducedcompared to the starting H₃ O⁺ mordenite.

Four samples of the Sn⁺² substituted sample described above were treatedin the following manner. One sample was titrated with 0.1N NaOHsolution, filtered, washed and analyzed. A second sample was placed into3.5M NH₄ Cl solution, filtered, washed and analyzed. A third sample wastreated at pH 9.0 with NH₄ OH solution, filtered, washed and analyzed. Afinal sample was treated in 3.5M CaCl₂ solution, filtered, washed andanalyzed. The chemical analysis data for the four samples are shownbelow:

    ______________________________________                                        Treatment:      NaOH    NH.sub.4 Cl                                                                           NH.sub.4 OH                                                                          CaCl.sub.2                             ______________________________________                                        SiO.sub.2 /Al.sub.2 O.sub.3 :                                                                 31.30   32.27   30.32  33.01                                  Cat. Eq., M.sup.+ /Al:                                                                        1.73    1.05    1.12   0.89                                   Cat. Eq., M.sup.+ /(Al + 2Sn):                                                                0.89    0.62    0.62   0.44                                   ______________________________________                                    

Ion exchange of the Sn⁺² substituted mordenite shows a substantialexcess in cations relative to the amount of aluminum contained in theframework; particularly for the NaOH treated sample, while theCa-exchanged sample did not exchange well. The increased ion exchangecapacity indicates that Sn⁺² in the framework also requires a cation. Itwas noticed that as the pH of the exchange is increased, the ionexchange capacity increases as well. This indicates that the originalcations balancing the negative charges on the Sn⁺² in the framework areprotons. The protons are strongly held by the Sn⁺², making the materialweakly acidic, thus requiring the higher pH to exchange the protons.

EXAMPLE 18

Fifty nine gm. H₃ O⁺ mordenite, containing 0.0539 moles Al₂ O₃, wasslurried in 500 ml distilled water and heated at 75° C. A 200 ml.solution containing 0.0913 moles of SnF₂ and 0.0915 moles NH₄ HF₂ inwater was added continuously at a rate of 2.5 ml. per minute. The amountof Sn⁺² added was sufficient to remove and replace 85% of the frameworkaluminum in the zeolite. The initial pH of the H₃ O⁺ mordenite was 2.68,which decreased to 2.27 at the end of the addition of the SnF₂ solution.Following the addition, the slurry was digested at 95° C. for 3 hours,filtered and washed free of soluble aluminum species and fluoride. Theresulting product was colorless and contained 6.95 wt. % SnO; the SiO₂/A₂ O₃ was 31.0, (the starting ratio of the H₃ O⁺ mordenite was 16.4).The product properties are compared to the starting H₃ O⁺ mordenite inthe following Table X:

                  TABLE X                                                         ______________________________________                                                       Starting    LZ-252                                                            H.sub.3 O.sup.+  mordenite                                                                Product                                            ______________________________________                                        SiO.sub.2 /Al.sub.2 O.sub.3 :                                                                  16.45         31.03                                          Cation Equivalent, M.sup.+ /Al:                                                                0.08          0.68                                           Cation Equivalent,                                                                             0.08          0.39                                           M.sup.+ /(Al + 2Sn):                                                          wt. % Sn.sup.+2 as SnO:                                                                        0             6.95                                           wt. % fluoride:  0             0.07                                           X-ray Crystallinity, %:                                                                        100           83                                             Asym. Stretch, cm.sup.-1 :                                                                     1082          1086                                           Sym. Stretch, cm.sup.-1 :                                                                      797           806                                            Absorbance at 3710 cm.sup.-1 :                                                                 0.403         0.280                                          "z" value:       0.171         0.119                                          ______________________________________                                    

The data in the above Table indicate that Sn⁺² has substituted into thezeolite framework. The X-ray crystallinity value for the substitutedproduct remains high and the amount of defects in the structure arereduced compared to the starting H₂ O⁺ mordenite.

Four samples of the Sn⁺² substituted sample described above were treatedin the following manner. One sample was treated in 3.5M NaCl andtitrated with 1.0N NaOH solution to pH 12, filtered, washed andanalyzed. A second sample was placed into 3.5M KCl solution and titratedto pH 12 with 1.0 KOH, filtered, washed and analyzed. A third sample wastreated at pH 10.0 with 10N NH₄ OH solution, filtered, washed andanalyzed. A final sample was treated in 3.5M LaCl₃ solution, filtered,washed and analyzed. The chemical analysis data for the four samples areshown below:

    ______________________________________                                        Treatment:      NaOH    KOH     NH.sub.4 OH                                                                          LaCl.sub.3                             ______________________________________                                        SiO.sub.2 /Al.sub.2 O.sub.3 :                                                                 31.03   33.92   33.36  32.40                                  Cat. Eq., M.sup.+ /Al:                                                                        1.83    2.09    1.38   0.70                                   Cat. Eq., M.sup.+ /(Al + 2Sn):                                                                0.89    0.92    0.62   0.31                                   ______________________________________                                    

Ion exchange of the Sn⁺² substituted mordenite shows a substantialexcess in cations relative to the amount of aluminum contained in theframework; particularly for the two samples titrated to pH 12. TheLa-exchanged sample did not exchange well, and the NH₄ ⁺ exchanged onlypart of the Sn⁺² protons. As stated above, the increased ion exchangecapacity indicates that Sn⁺² in the framework also requires a cation.Increased exchange capacity with increasing pH indicates that theoriginal cations balancing the negative charges on the Sn⁺² in theframework are protons which are strongly held by the Sn⁺², making thematerial weakly acidic.

EXAMPLE 19

Five gm. H₃ O⁺ mordenite, containing 0.0062 moles Al_(O) ₃, was slurriedin 100 ml distilled water and heated at 75° C. A 50 ml. solutioncontaining 0.0061 moles of SnF₄ and 0.0061 moles of NH₄ HF₂ in water wasadded in 5 ml. increments every 5 minutes. The amount of Sn⁺⁴ added wassufficient to remove and replace 50% of the framework aluminum in thezeolite. The initial pH of the H₃ O⁺ mordenite was 2.09, which droppedto 1.98 during the addition of the SnF₄ solution, but was 2.1 at the endof the addition. Following the addition, the slurry was digested at 75°C. for 1 hour, filtered and washed free of soluble aluminum species andfluoride. The resulting product contained 16.34 wt. % SnO₂ ; the SiO₂/Al₂ O₃ was 34.8, (the starting ratio of the H₃ O⁺ mordenite was 11.7);there was a small decrease in absorbance in the hydroxyl region of theinfrared spectrum measured at 3710 cm⁻¹ attributed to hydrogen bonded OHgroups in dealuminated sites. The data indicate substitution of Sn⁺⁴ inframework tetrahedral sites. Comparison of the product properties withthe starting H₃ O⁺ mordenite is shown in the following Table Y:

                  TABLE Y                                                         ______________________________________                                                       Starting    LZ-252                                                            H.sub.3 O.sup.+  mordenite                                                                Product                                            ______________________________________                                        SiO.sub.2 /Al.sub.2 O.sub.3 :                                                                  11.67         34.82                                          Cation Equivalent, M.sup.+ /Al:                                                                0.06          0.56                                           wt. % Sn.sup.+4 :                                                                              0             16.34                                          wt. % fluoride:  0             0.24                                           X-ray Crystallinity, %:                                                                        100           62                                             Asym. Stretch, cm.sup.-1 :                                                                     1069          1084                                           Sym. Stretch, cm.sup.-1 :                                                                      796           810                                            Absorbance at 3710 cm.sup.-1 :                                                                 0.203         0.172                                          "z" value:       0.086         0.073                                          McBain O.sub.2, wt. %:                                                                         19.7          171                                            McBain H.sub.2 O, wt. %:                                                                       16.3          9.5                                            McBain neopentane, wt. %:                                                                      6.1           3.3                                            McBain SF.sub.6, wt. %:                                                                        12.3          7.9                                            ______________________________________                                    

The data in the above Table indicate that Sn⁺⁴ has substituted into thezeolite framework, but there has been some loss in crystallinity asevidenced by the reduced adsorption capacities.

EXAMPLE 20

Ten gm. NH₄ Y, containing 0.0215 moles of Al₂ O₃ was slurried in 100 mldistilled H₂ O and heated at 75° C. A 25 ml. solution containing 0.0108moles of SnF₄ and 0.0107 moles of NH₄ HF₂ in water was added in 1.4 ml.increments approximately every 5 minutes. The amount of Sn⁺⁴ added wassufficient to remove and replace 25% of the framework aluminum in thezeolite. The initial pH of the slurry at 75° C. was 4.35, whichdecreased to 4.21 during the addition and was 4.54 at the end of theaddition. Following the addition, the slurry was digested for threehours at 95° C., filtered and washed free of soluble aluminum speciesand fluoride. The resulting product contained 14.56 wt. % SnO₂ ; theSiO₂ /Al₂ O₃ was 7.16 (the starting ratio of the NH₄ Y was 5.09). Therewas substitution of Sn⁺⁴ and the sample was approximately 28%dealuminated. Comparison of the properties of the product zeolite withthe starting NH₄ Y is shown in the following Table Z:

                  TABLE Z                                                         ______________________________________                                                      Starting NH.sub.4 Y                                                                      Product Zeolite                                      ______________________________________                                        SiO.sub.2 /Al.sub.2 O.sub.3 :                                                                 5.09         7.16                                             Cation Equivalent, M.sup.+ /Al:                                                               1.05         0.99                                             wt. % SnO.sub.2 :                                                                             0            14.56                                            wt. % fluoride: 0            0.14                                             X-ray Crystallinity, %:                                                                       100          40                                               Asym. Stretch, cm.sup.-1 :                                                                    1020         1032                                             Sym. Stretch, cm.sup.-1 :                                                                     786          791                                              Absorbance at 3710 cm.sup.-1 :                                                                0.038        0.124                                            "z" value:      0.016        0.053                                            McBain O.sub.2, wt. %:                                                                        32.1         23.5                                             McBain H.sub.2 O, wt. %:                                                                      29.4         22.1                                             McBain neopentane, wt. %:                                                                     --           10.2                                             McBain SF.sub.6, wt. %:                                                                       --           17.5                                             n-butane cracking, k.sub.A :                                                                  1.9          2.0                                              ______________________________________                                    

The data indicate that Sn⁺⁴ is substituted into the tetrahedral sites inthe framework. The low k_(A) value for the product in butane cracking isconsistent with this conclusion, since SnO₂ deposited in the pores ofthe zeolite would show severe cracking activity due to presence ofaccessible Sn ions.

EXAMPLE 21

Five gm. NH₄ -L zeolite, containing 0.0095 moles Al₂ O₃, was slurried in100 ml distilled water and heated at 75° C. A 50 ml. solution containing0.0095 moles of SnF₄ and 0.0095 moles of NH₄ HF₂ in water was added in 5ml. increments every 5 minutes. The amount of Sn⁺⁴ added was sufficientto remove and replace 50% of the framework aluminum in the zeolite. Theinitial pH of the NH₄ -L slurry was 6.55, which dropped to 2.38 duringthe addition of the SnF₄ solution, and was 2.38 at the end of theaddition. Following the addition, the slurry was digested at 75° C. for1 hour, filtered and washed free of soluble aluminum species andfluoride. The pH at the end of the digestion was 2.93. The resultingproduct contained 17.04 wt. % Sn measured as SnO₂ ; the SiO₂ /Al₂ O₃ was8.45, (the starting ratio of the NH₄ -L was 5.92). There was an increasein absorbance in the hydroxyl region of the infrared spectrum measuredat 3710 cm⁻¹ attributed to hydrogen bonded OH groups in dealuminatedsites. However, the measured amount of defects in the structure wereinsufficient to account for the amount of dealumination. The dataindicate substitution of Sn⁺⁴ in framework tetrahedral sites. Comparisonof the product properties with the starting NH₄ -L is shown in thefollowing Table A1:

                  TABLE A1                                                        ______________________________________                                                      Starting NH.sub.4 -L                                                                     LZ-273 Product                                       ______________________________________                                        SiO.sub.2 /Al.sub.2 O.sub.3 :                                                                 5.92         8.45                                             Cation Equivalent, M.sup.+ /Al:                                                               0.99         1.00                                             wt. % Sn.sup.+4 :                                                                             0            17.04                                            wt. % fluoride: 0            0.34                                             X-ray Crystallinity, %:                                                                       100          40                                               Asym. Stretch, cm.sup.-1 :                                                                    1028         1032                                             Sym. Stretch, cm.sup.-1 :                                                                     770          771                                              Absorbance at 3710 cm.sup.-1 :                                                                0.078        0.220                                            "z" value:      0.033        0.093                                            McBain O.sub.2, wt. %:                                                                        16.2         16.6                                             McBain H.sub.2 O, wt. %:                                                                      18.0         15.3                                             McBain neopentane, wt. %:                                                                     --           7.9                                              McBain SF.sub.6, wt. %:                                                                       --           11.8                                             n-butane cracking, k.sub.A :                                                                  1.3          2.9                                              ______________________________________                                    

The data in the above Table indicate that Sn⁺⁴ has substituted into thezeolite framework. Loss of structure as evidenced by the reduced X-raycrystallinity values can be explained by the incorporation of the largerSn⁺⁴ ion into the zeolite framework and by fluorescence of that ion. Amore accurate indication of crystal retention is evidenced by theretention of adsorption capacities, which show that both void volume andpore size have been maintained, despite incorporation of 17 wt. % ofSnO₂ into the zeolite. The n-butane cracking activity value, k_(A) hasalso increased.

EXAMPLE 22

Ten gm. NH₄ L, containing 0.0190 moles of Al₂ O₃ was slurried in 100 mldistilled H₂ O and heated at 75° C. A 25 ml. solution containing 0.0025moles of SnF₄ and 0.0025 moles of NH₄ HF₂ in water was added in 1 mlincrements every 5 minutes. The amount of Sn⁺⁴ added was sufficient toremove and replace 7% of the framework aluminum in the zeolite. Theinitial pH of the slurry at 75° C. was 5.73, which decreased to 2.98during the addition and was 2.98 at the end of the addition. Followingthe addition, the slurry was digested for 1 hour at 75° C., filtered andwashed free of soluble aluminum species and fluoride. The resultingproduct contained 3.44 wt. % Sn measured as SnO₂ ; the SiO₂ /Al₂ O₃ was6.95 (the starting ratio of the NH₄ L was 5.92). Comparison of theproperties of the product zeolite with the starting NH₄ L is shown inthe following Table A2:

                  TABLE A2                                                        ______________________________________                                                      Starting NH.sub.4 -L                                                                     LZ-273 Product                                       ______________________________________                                        SiO.sub.2 /Al.sub.2 O.sub.3 :                                                                 5.92         6.95                                             Cation Equivalent, M.sup.+ /Al:                                                               0.99         0.95                                             wt. % SnO.sub.2 :                                                                             0            3.44                                             wt. % fluoride: 0            0.05                                             X-ray Crystallinity, %:                                                                       100          91                                               Asym. Stretch, cm.sup.-1 :                                                                    1028         1029                                             Sym. Stretch, cm.sup.-1 :                                                                     770          769                                              Absorbance at 3710 cm.sup.-1 :                                                                0.078        0.080                                            "z" value:      0.033        0.034                                            McBain O.sub.2, wt. %:                                                                        16.2         17.2                                             McBain H.sub.2 O, wt. %:                                                                      18.0         17.1                                             McBain neopentane, wt. %:                                                                     --           2.7                                              McBain SF.sub.6, wt. %:                                                                       --           4.3                                              n-butane cracking, k.sub.A :                                                                  1.3          2.7                                              ______________________________________                                    

The data indicate that Sn⁺⁴ is substituted into the tetrahedral sites inthe framework.

EXAMPLE 23

250 gm. NH₄ -L zeolite, containing 0.4455 moles Al₂ O₃, was slurried in2.5 liters distilled water and heated at 75° C. A 250 ml. solutioncontaining 0.0632 moles of SnF₄ and 0.0633 moles of NH₄ HF₂ in water wasadded at a constant rate of 5 ml. every 5 minutes by means of aperistaltic pump. The amount of Sn⁺⁴ added was sufficient to remove andreplace 7% of the framework aluminum in the zeolite. The initial pH ofthe NH₄ -L slurry was 7.93. Following addition of the SnF₄ solution, thepH was 3.59. The slurry was digested at 75° C. for 1 hour, filtered andwashed free of soluble aluminum species and fluoride. The pH at the endof the digestion was 3.75. The resulting product contained 3.19 wt. % Snmeasured as SnO₂ ; the SiO₂ /A₂ O₃ was 6.95, (the starting ratio of theNH₄ -L was 6.74). There was a small increase in absorbance in thehydroxyl region of the infrared spectrum measured at 3710 cm⁻¹attributed to hydrogen bonded OH groups in dealuminated sites. However,the measured amount of defects in the structure were insufficient toaccount for the amount of dealumination. The data indicate substitutionof Sn⁺⁴ in framework tetrahedral sites. Comparison of the productproperties with the starting NH₄ -L is shown in the following Table A3:

                  TABLE A3                                                        ______________________________________                                                      Starting NH.sub.4 -L                                                                     LZ-273 Product                                       ______________________________________                                        SiO.sub.2 /Al.sub.2 O.sub.3 :                                                                 6.74         6.95                                             Cation Equivalent, M.sup.+ /Al:                                                               0.98         0.95                                             wt. % Sn.sup.+4 :                                                                             0            3.19                                             wt. % fluoride: 0            0.08                                             X-ray Crystallinity, %:                                                                       100          84                                               Asym. Stretch, cm.sup.-1 :                                                                    1033         1032                                             Sym. Stretch, cm.sup.-1 :                                                                     772          773                                              Absorbance at 3710 cm.sup.-1 :                                                                0.058        0.082                                            "z" value:      0.025        0.035                                            McBain O.sub.2, wt. %:                                                                        16.4         16.5                                             McBain H.sub.2 O, wt. %:                                                                      17.1         16.2                                             McBain neopentane, wt. %:                                                                     6.3          6.7                                              McBain SF.sub.6, wt. %:                                                                       13.8         13.3                                             n-butane cracking, k.sub.A :                                                                  3.4          3.6                                              ______________________________________                                    

The data in the above Table indicate that Sn⁺⁴ has substituted into thezeolite framework.

EXAMPLE 24

250 gm. NH₄ -L zeolite, containing 0.4455 moles Al₂ O₃, was slurried in2.5 liters distilled water and heated at 75° C. A 250 ml. solutioncontaining 0.0105 moles of SnF₄ and 0.0106 moles of NH₄ HF₂ in water wasadded at a constant rate of 1.4 ml. every 5 minutes by means of aperistaltic pump. The amount of Sn⁺⁴ added was sufficient to remove andreplace 1.2% of the framework aluminum in the zeolite. The initial pH ofthe NH₄ -L slurry was 7.98. Following addition of the SnF₄ solution, thepH was 4.12. The slurry was digested at 75° C. for 1 hour, filtered andwashed free of soluble aluminum species and fluoride. The pH at the endof the digestion was 4.49. The resulting product contained 0.78 wt. % Snmeasured as SnO₂ ; the SiO₂ /Al₂ O₃ was 6.56, (the starting ratio of theNH₄ -L was 6.74). There was no change in absorbance in the hydroxylregion of the infrared spectrum measured at 3710 cm⁻¹ attributed tohydrogen bonded OH groups in dealuminated sites. The data indicatesubstitution of Sn⁺⁴ in framework tetrahedral sites. Comparison of theproduct properties with the starting NH₄ -L is shown in the followingTable A4:

                  TABLE A4                                                        ______________________________________                                                      Starting NH.sub.4 -L                                                                     LZ-273 Product                                       ______________________________________                                        SiO.sub.2 /Al.sub.2 O.sub.3 :                                                                 6.74         6.56                                             Cation Equivalent, M.sup.+ /Al:                                                               0.98         0.93                                             wt. % Sn.sup.+4 :                                                                             0            0.78                                             wt. % fluoride: 0            0.01                                             X-ray Crystallinity, %:                                                                       100          93                                               Asym. Stretch, cm.sup.-1 :                                                                    1033         1002                                             Sym. Stretch, cm.sup.-1 :                                                                     772          774                                              Absorbance at 3710 cm.sup.-1 :                                                                0.058        0.058                                            "z" value:      0.025        0.025                                            McBain O.sub.2, wt. %:                                                                        16.4         16.8                                             McBain H.sub.2 O, wt. %:                                                                      17.1         17.0                                             McBain neopentane, wt. %:                                                                     6.3          6.6                                              McBain SF.sub.6, wt. %:                                                                       13.8         13.6                                             n-butane cracking, k.sub.A :                                                                  3.4          2.8                                              ______________________________________                                    

The data in the above Table indicate that Sn⁺⁴ has substituted into thezeolite framework.

PROCESS APPLICATIONS

The molecular sieves compositions in this invention have unique surfacecharacteristics making them useful as molecular sieves and as catalystor as bases for catalysts in a variety of separation, hydrogenconversion and oxidative combustion processes. These composition can beimpregnated or otherwise associated with catalytically active metals bythe numerous methods known in the art and used, for example, infabricating catalysts compositions containing alumina or aluminosilicatematerials.

The instant molecular sieve compositions may be employed for separatingmolecular species in admixture with molecular species of a differentdegree of polarity or having different kinetic diameters by contactingsuch mixtures with a molecular sieve composition having pore diameterslarge enough to adsorb at least one but not all molecular species of themixture based on the polarity of the adsorbed molecular species and/orits kinetic diameter. When the instant compositions are employed forsuch separation processes the compositions are at least partiallyactivated whereby some molecular species selectively enter theintracrystalline pore system thereof.

The hydrocarbon conversion reactions which may be catalyzed by theinstant molecular sieve compositions include; cracking, hydrocracking;alkylation of both the aromatic and isoparaffin types; isomerization(including xylene isomerization); polymerization; reforming;hydrogenation; dehydrogenation; transalkylation; dealkylation; andhydration.

When catalyst composition containing the instant molecular sievecompositions also contains a hydrogenation promoter, such promoter maybe platinum, palladium, tungsten, nickel or molybdenum and may be usedto treat various petroleum stocks including heavy petroleum residualstocks, cyclic stocks and other hydrocrackable charge stocks. Thesestocks can be hydrocracked at temperatures in the range of between about400° F. and about 825° F. using molar ratios of hydrogen to hydrocarbonin the range of between about 2 and about 80, pressures between about 10and about 3500 p.s.i.g., and a liquid hourly space velocity (LHSV) ofbetween about 0.1 and about 20, preferably between about 1.0 and about10.

Catalyst compositions containing the instant molecular sievecompositions may also be employed in reforming processes in which thehydrocarbon feedstocks contact the catalyst at temperatures betweenabout 700° F. and about 1000° F., hydrogen pressures of between about100 and about 500 p.s.i.g., LHSV values in the range between about 0.1and about 10 and hydrogen to hydrocarbon molar ratios in the rangebetween about 1 and about 20, preferably between about 4 and about 12.

Further, catalysts containing the instant molecular sieve compositionswhich also contain hydrogenation promoters, are also useful inhydroisomerization processes wherein the feedstock(s), such as normalparaffins, is converted to saturated branched-chain isomers.Hydroisomer-ization processes are typically carried out at a temperaturebetween about 200° F. and about 600° F., preferably between about 300°F. and about 550° F. with an LHSV value between about 0.2 and about 1.0.Hydrogen is typically supplied to the reactor in admixture with thehydrocarbon feedstock in molar proportions of hydrogen to the feedstockof between about 1 and about 5.

Catalyst compositions similar to those employed for hydrocracking andhydroisomerization may also be employed at between about 650° F. andabout 1000° F., preferably between about 850° F. and about 950° F. andusually at somewhat lower pressures within the range between about 15and about 50 p.s.i.g. for the hydroisomerization of normal paraffins.Preferably the paraffin feedstock comprises normal paraffins having acarbon number range of C₇ -C₂₀. The contact time between the feedstockand the catalyst is generally relatively short to avoid undesirable sidereactions such as olefin polymerization and paraffin cracking. LHSVvalues in the range between about 0.1 and about 10, preferably betweenabout 1.0 and about 6.0 are suitable.

The low alkali metal content of the instant compositions make themparticularly well suited for use in the conversion of alkylaromaticcompounds, particularly for use in the catalytic disproportionation oftoluene, xylene trimethylbenzenes, tetramethylbenzenes and the like. Insuch disproportionation processes it has been observed thatisomerization and transalkylation can also occur. The catalystscontaining the instant molecular sieve compositions and employed forsuch processes will typically include Group VIII noble metal adjuvantsalone or in conjunction with Group VI-B metals such as tungsten,molybdenum and chromium which are preferably included in such catalystcompositions in amounts between about 3 and about 15 weight-percent ofthe overall catalyst composition. Extraneous hydrogen can, but need notbe present in the reaction zone which is maintained at a temperaturebetween about 400° and about 750° F., pressures in the range betweenabout 100 and about 2000 p.s.i.g. and LHSV values in the range betweenabout 0.1 and about 15.

Catalysts containing the instant molecular sieve compositions may beemployed in catalytic cracking processes wherein such are preferablyemployed with feedstocks such as gas oils, heavy naphthas, deasphaltedcrude oil residues etc. with gasoline being the principal desiredproduct. Temperature conditions are typically between about 850° andabout 1100° F., LHSV values between about 0.5 and about 10 pressureconditions are between about 0 p.s.i.g. and about 50 p.s.i.g.

Catalysts containing the instant molecular sieve compositions may beemployed for dehydrocyclization reactions which employ paraffinichydrocarbon feedstocks, preferably normal paraffins having more than 6carbon atoms, to form benzene, xylenes, toluene and the like.Dehydrocyclization processes are typically carried out using reactionconditions similar to those employed for catalytic cracking. For suchprocesses it is preferred to use a Group VIII non-noble metal cationsuch as cobalt and nickel in conjunction with the molecular sievecomposition.

Catalysts containing the instant molecular sieve compositions may beemployed in catalytic dealkylation where paraffinic side chains arecleaved from aromatic nuclei without substantially hydrogenating thering structure at relatively high temperatures in the range betweenabout 800° F. and about 1000° F. at moderate hydrogen pressures betweenabout 300 and about 1000 p.s.i.g. with other conditions being similar tothose described above catalytic hydrocracking. Catalysts employed forcatalytic dealkylation are of the same type described above inconnection with catalytic dehydrocyclization. Particularly desirabledealkylation reactions contemplated herein include the conversion ofmethylnaphthalene to naphthalene and toluene and/or xylenes to benzene.

Catalysts containing the instant molecular sieve compositions may beused in catalytic hydrofining wherein the primary objective is toprovide for the selective hydrodecomposition of organic sulfur and/ornitrogen compounds without substantially affecting hydrocarbon moleculespresent therewith. For this purpose it is preferred to employ the samegeneral conditions described above for catalytic hydrocracking. Thecatalysts are the same typically of the same general nature as describedin connection with dehydrocyclization operations. Feedstocks commonlyemployed for catalytic hydroforming include: gasoline fractions;kerosenes; jet fuel fractions; diesel fractions; light and heavy gasoils; deasphalted crude oil residua; and the like. The feedstock maycontain up to about 5 weight-percent of sulfur and up to about 3weight-percent of nitrogen.

Catalysts containing the instant molecular sieve compositions may beemployed for isomerization processes under conditions similar to thosedescribed above for reforming although isomerization processes tend torequire somewhat more acidic catalysts than those employed in reformingprocesses. Olefins are preferably isomerized at temperatures betweenabout 500° F. and about 900° F., while paraffins, naphthenes and alkylaromatics are isomerized at temperatures between about 700° F. and about1000° F. Particularly desirable isomerization reactions contemplatedherein include the conversion of n-heptane and/or n-octane toisoheptanes, iso-octanes, butane to iso-butane, methylcyclopentane tocyclohexane, meta-xylene and/or ortho-xylene to para-xylene, 1-butene to2-butene and/or isobutene, n-hexene to isohexane, cyclohexane tomethylcyclopentene etc. The preferred cation form is a combination of amolecular sieve of this invention and polyvalent metal compounds (suchas sulfides) of metals of Group II-A, Group II-B and rare earth metals.For alkylation and dealkylation processes the instant molecular sievecompositions having pores of at least 5 are preferred. When employed fordealkylation of alkyl aromatics, the temperature is usually at least350° F. and ranges up to a temperature at which substantial cracking ofthe feedstock or conversion products occurs, generally up to about 700°F. The temperature is preferably at least 450° F. and not greater thanthe critical temperature of the compound undergoing dealkylation.

Pressure conditions are applied to retain at least the aromatic feed inthe liquid state. For alkylation the temperature can be as low as 250°F. but is preferably at least 350° F. In alkylation of benzene, tolueneand xylene, the preferred alkylation agents are olefins such as ethyleneand propylene.

The molecular sieve compositions of this invention may be employed inconventional molecular sieving processes as heretofore have been carriedout using aluminosilicate, aluminophosphate or other commonly employedmolecular sieves. The instant compositions are preferably activated,e.g. calcined in air or nitrogen, prior to their use in a molecularsieve process.

The molecular sieve compositions of this invention are also useful asadsorbents and are capable of separating mixtures of molecular speciesboth on the basis of molecular size (kinetic diameters) and based on thedegree of polarity of the molecular species. When the separation ofmolecular species is based upon selective adsorption based on molecularsize, the instant molecular sieve composition is chosen in view of thedimensions of its pores such that at least the smallest molecularspecies of the mixture can enter the intracrystalline void space whileat least the largest species is excluded. When the separation is basedon degree of polarity it is generally the case that the more hydrophilicmolecular sieve composition will preferentially adsorb the more polarmolecular species of a mixture having different degrees of polarity eventhough both molecular species can communicate with the pore system ofthe molecular sieve composition.

EXAMPLE 25

This is a comparative example which reproduces Example 1 of CanadianPatent 1,127,134. Solution 1 containing 48 g of sodium silicate and 60 gof distilled water was prepared in a 250 mL, 3-necked, round bottomedflask. The flask was equipped with an electric stirrer and placed in aheating mantle with a temperature controller. A second solution(solution 2) was prepared by placing 82 g of water into a 150 mL beakerand then adding to the water 6 g of tetrapropyl ammonium bromide, 4 g ofconcentrated sulfuric acid and 2.45 g of potassium chromium sulfate(CrK(SO₄)₂.12H₂ O and 0.02 g of H-ZSM-5 seed. Upon addition of thepotassium chromium sulfate, the solution turned dark blue.

Solution 2 was added to sodium 1 with stirring resulting in agreenish-blue gelatinous and thick mixture. Stirring was increased untilthe mixture began to thin. At this point the mixture or slurry washeated to 96° C. which thinned out the slurry further. The slurry wasstirred at 96° C. for 6 days. During this time, the slurry became greenand finally a chalky green in color. After 6 days, the slurry wascentrifuged to separate the solids and liquid. After the liquid wasdecanted, the solids were washed by mixing with distilled water and thencentrifuged again. A total of 1,000 mL of water were used to wash thesolids.

It was observed that after centrifugation, the solid product consistedof two distinct layers. The smaller top layer was dark green while thelarger layer was light green in color. The upper layer readily dispersedin the wash water. After the last wash the dark green layer wasseparated from the bottom layer by rinsing with a small amount ofadditional distilled water and the solids collected (Product A). Theother, light green fraction of the sample was labeled Product B. Bothsolid products were dried in an air-purged oven at 70° C. for 16 hours.The major fraction of Product B was further calcined in a muffle furnaceat 500° C. for 12 hours and cooled. It was labeled Product C. Followingthe calcination, the light green color became light yellow.

The respective Products had the following properties.

    ______________________________________                                                    Product A  Product B  Product C                                   Color       Dark Green Light Green                                                                              Light Yellow                                ______________________________________                                        X-ray Crystallinity,                                                                      54         90         >100                                        % ZSM-5 Relative                                                              to a Standard                                                                 Chemical Analyses                                                             (TPA).sub.2 O, wt. %                                                                      7.86       10.84       0.00                                       Cr.sub.2 O.sub.3, wt. %                                                                   14.25      0.59        0.66                                       SiO.sub.2 /Al.sub.2 O.sub.3                                                               260.0      321.6      316.0                                       Ratios:                                                                       (TPA).sub.2 O/Al.sub.2 O.sub.3                                                            4.2        6.2        0.0                                         (Na.sub.2 O/Al.sub.2 O.sub.3                                                              9.5        5.1        4.8                                         K.sub.2 O/Al.sub.2 O.sub.3                                                                0.7        0.2        0.2                                         Cation Equivalents:                                                           M.sup.+ /Al 14.4       11.5       5.0                                         M.sup.+ /Al + Cr                                                                          0.7        6.2        2.8                                         ______________________________________                                    

The dark green material, Product A, contained most of the chromium. Ifsolids separation had been effected by filtration instead ofcentrifugation, it would have been homogeneously blended with the bulkof the sample and would not have been easily identified. On drying itbecame a chunky mass. Besides chromium oxide, product A contains themajor fraction of the potassium and sodium, and also contains a greateraluminum content. This is consistent with precipitation of hydrolyzedchromium species due to the high pH of the synthesis gel. Ondehydration, the mass coalesces into a glue like material, causing theformation of the chunky mass.

All three products were examined by Scanning Electron Microscopy, (SEM).Product A showed small crystals of ZSM-5 packed together inside anamorphous mass. The amorphous mass was mostly chromium oxide while thezeolite crystals showed very little chromium oxide. The presence of thechromium oxide can be explained solely by the adherence of chromiumoxide particles on the surface of the crystals.

Product B and Product C were similar to Product A in that largercrystals of ZSM-5 were found and a few showed some nondescript oramorphous particles adhering to the outside surface of the zeolitecrystals. The amorphous particles contained high levels of chromium. Thezeolite crystals were almost chromium free, with the chromium foundmostly on or at the surface of the crystals.

All three products were examined by Analytical Transmission ElectronMicroscopy dry-brush techniques, (ATEM), with thin sections of bothProducts B and C also examined by the microtome technique. The dry-brushsamples confirmed the findings of the SEM examination. Chromium wasdetected in amorphous masses outside the zeolite crystals. When theclean surfaces of the zeolite crystals were examined, only very tracequantities of chromium were detected. Examination of the thin sectionsof Product B, the light green material that had been dried only, did notshow any detectable chromium in the interior portions of the zeolitecrystals. However, trace levels of chromium were detected in thecalcined material, Product C. The only explanation for the trace amountsof chromium is that the chromium was present with the template duringsynthesis. Thus, it was included inside the zeolite channels and not inthe framework. This quantity of chromium is too low to detect by ATEM(2300 ppm), but upon calcination, the template is removed and thechromium agglomerates, thereby making it barely detectable by ATEM.

The only conclusion that can be drawn from the SEM and ATEM analysis isthat chromium was not incorporated into the ZSM-5 framework. This isexactly what one would expect based on the high pH of the synthesis gel.The bulk of the chromium is precipitated as a hydrolyzed species whichadheres to the outside surface of the zeolite crystals. On drying orcalcining, the chrome agglomerates into amorphous particles thatcontinue to adhere to the outside surface of the zeolite crystals. Thebarely detectable chromium found on the inside of the zeolite crystalsare present as occluded chromium owing to the chromium being associatedwith the templating agent during synthesis. There was no evidence oftetrahedral chromium in the framework.

We claim as our invention:
 1. A molecular sieve having athree-dimensional microporous framework structure which has a unitempirical formula on an anhydrous basis of:

    (Cr.sub.w Al.sub.x Si.sub.y)O.sub.2

where w, x and y are the mole fractions of chromium, aluminum andsilicon, respectively, present as the framework tetrahedral oxide unitssaid mole fractions being such that they are within the triagonal areadefined by points A, B, and C of FIG. 1, which points have the followingvalues of w, x and y

    ______________________________________                                        Point    w             x      y                                               ______________________________________                                        A        0.49          0.01   0.50                                            B        0.01          0.49   0.50                                            C        0.01          0.01    0.98.                                          ______________________________________                                    


2. A molecular sieve having a three-dimensional microporous frameworkstructure which has a unit empirical formula on an anhydrous basis of

    [Al.sub.u Si.sub.v Cr.sub.w □.sub.z ]O.sub.2

where u is the mole fraction of aluminum and ranges from about 0.01 toabout 0.5, v is the mole fraction of silicon and ranges from about 0.5to about 0.98, w is the mole fraction of chromium and ranges from about0.01 to about 0.49, □ is framework defect sites and z is the molefraction of defect sites in the framework and ranges from greater thanzero to about 0.2 characterized in that the aluminum, silicon and tinare present as tetrahedral oxide units in the framework structure. 3.The molecular sieve of claim 1 having the characteristic x-ray powderdiffraction pattern of zeolite Y.
 4. The molecular sieve of claim 1having the characteristic x-ray powder diffraction pattern of zeolitemordenite.
 5. The molecular sieve of claim 1 having the characteristicx-ray powder diffraction pattern of LZ-202.
 6. The molecular sieve ofclaim 1 having the characteristic x-ray powder diffraction pattern of L.